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OCTOBER 2023 ISSN 1030-2662 10 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1390 12 INC GST INC GST 1kW+ Class-D Amplifier make it yourself using pre-built modules Photographing Electronics how to take quality photographs 2m Test Signal Generator CW and FM in the VHF band Programming SMD Micros with our reconfigurable adaptors The History of Electronics Inventors & their Inventions Prototyping Accessories GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. PB8815 QUICK AND EASY PROTOTYPING HP9572 MAKE YOUR BREADBOARD PROTOTYPE PERMANENT Solderless Breadboards PB8820 FROM 5 $ 6 models available. PB8815 - PB8832 Breadboard Jumper Kit 70 Pieces PB8850 $11.95 95 Breadboard Layout Prototyping Boards WC6027 Make your own circuit boards Etch Resistant Pen • 0.6mm tip TM3002 $6.95 FROM 595 $ 400 Hole HP9570 | 862 Hole HP9572 150mm Jumper Leads WC6024 - WC6028 FROM $6.95 Blank Fibreglass Copper Sided PCBs • 4 sizes available HP9510 - HP9515 FROM $6.95 HP9570 20 Piece PCB Wash Micro Drill Set Defluxing Solution • Sizes: 0.3 - 1.6mm • 1 Litre Bottle TD2406 $13.95 NA1070 $15.95 8 x 25m Hook-Up Wire Rolls 26AWG WH3009 $50.95 MAKE PCBS IN 4 EASY STEPS. 1. PRINT/COPY 2. IRON ON 3. PEEL OFF 4. ETCH Press 'n' Peel Film 5 sheets of 215 x 280mm transfer film with full instructions. JUST 4495 $ HG9980 Shop at Jaycar for: • Soldering & Accessories • Components, Cables and Connectors • Magnifiers and Inspection Aids • Tools, Service Aids and Chemicals Explore our full range of prototyping accessories, in stock at over 110 stores, or 130 resellers or on our website. jaycar.com.au/prototyping 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Contents Vol.36, No.10 October 2023 12 The History of Electronics, Pt1 We go over the brilliant scientists and inventors who discovered every aspect of electronics technology. They made modern inventions like transistors, ICs and wireless communication possible. By Dr David Maddison Electronic inventions & inventors 36 How to Photograph Electronics Taking quality photographs is beneficial for both hobby and business projects, and modern cameras make this much easier. We detail the other steps you should take to improve your photgraphy via your technique, lighting and ‘studio’ setup. By Kevin Poulter Photography feature 1kW+ Class-D Mono Amplifier Page 28 Photographing Electronics how to take better photos 54 The Linshang LS172 Colorimeter This colorimeter is an affordable way to verify that you have the right colours when buying paint or doing a print project. All you need to do is place it over the colour you want to measure and it will do the rest. By Allan Linton-Smith Test & measurement equipment review 82 1.3in Monochrome OLED Display The 1.3in (33mm) OLED display module has a resolution of 128x64 pixels and is perfect as a display for an Arduino or Micromite project due to its wide availability, I2C interface and cost. By Jim Rowe Using electronic modules 28 1kW+ Class-D Amplifier, Pt1 This Class-D monoblock amplifier is built using a pre-made amplifier module and six inexpensive 24-25V switchmode supplies. It delivers up to 1.2kW into 2W loads or over 500W into 4W! By Allan Linton-Smith Audio project Page 36 Page 64 TQFP Programming Adaptors 2 Editorial Viewpoint 5 Mailbag 61 Circuit Notebook 71 Subscriptions 88 Online Shop 90 Serviceman’s Log 98 Vintage Radio 44 2m Test Signal Generator This test oscillator uses an AD9834 DDS to produce signals in the 2m band (144-148MHz, in 500kHz steps), either carrier-only (no modulation) or FM. It does all this on a compact PCB that fits in a 3D-printed enclosure. By Andrew Woodfield, ZL2PD Test & measurement project 64 TQFP Programming Adaptors Following on from our PIC Programming Adaptor last month, we show you how to program SMD micros in SOT-23-6 and (T)QFP from 32 to 100 pins using reconfigurable jigs with high-quality sockets. By Nicholas Vinen Microcontroller project 72 30V 2A Bench Supply, Mk2 – Pt2 In the final part of our series, we explain how to build, test and calibrate the Supply so that you can use it for powering circuits or development. By John Clarke Power supply project 1. Mini inverter to power a soldering iron 2. Improved gesture recognition software 3. Pi Pico W BackPack ‘analog’ clock 4. Automatic AI Doorman IJA Chi receiver by Ian Batty 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint Take mains safety seriously! We have been describing mains-powered projects in Silicon Chip since the first issue in November 1987. As far as we are aware, nobody has been seriously hurt by an accidental shock while building or operating such equipment. That good record extends back to the days of Electronics Australia, and I would like to keep it that way. I am writing this because we have seen evidence of constructors skipping critical safety steps in our assembly instructions, creating potentially hazardous devices. Part of the reason we have a good record is that our mains-powered projects include safety redundancy. The idea is that even if one or two things go wrong, the result should not be a shock hazard. To achieve this, we direct constructors do things like insulate all exposed mains conductors (even those that are usually inaccessible inside the case), use cable ties to bundle wires together (into separate mains and low-voltage bundles), anchor wires so they can’t float around inside the device, Earth all exposed metal, incorporate mains fuses and so on. Say a mains wire happens to break loose in one of our designs. As it’s cable tied to adjacent wires, it shouldn’t be able to move far enough to touch anything. If another wire or two breaks, maybe that bundle of wires could contact the Earthed case. In that case, the fuse should blow so the case doesn’t become live. You could lose this redundancy if you don’t follow our instructions fully. So, if you are building one of our mains-powered projects, please follow all the instructions carefully, even if you don’t understand why they are necessary. Remember that a poorly built device could be hazardous to anyone in your household who could come in contact with it. The steps we describe are not expensive, onerous or overly time-consuming. Some further advice: • Don’t take on a mains-powered project if you are inexperienced. Build a low-voltage device (or several) until you are confident in your assembly skills, including soldering, crimping, screwing, machining and so on. That way, when you build a mains-powered device, you will be confident that you will not make a bad solder joint or skip an important step. • If you are not fully confident in your abilities, get someone else who has more experience to help you. Even if they are not an expert, having a second pair of eyes and hands can be invaluable. They might spot something you missed or prevent you from making a mistake. • Respect mains voltages and keep your hands (and any uninsulated tools they hold) away from equipment that’s plugged into the mains, even if it is not switched on. Some conductors could still be live; something simple like a miswired extension cord or power point could make everything live, even with the Active conductor broken by a switch. • During testing, troubleshooting or calibration, adopt an approach of connecting equipment to the device, withdrawing physically from it, plugging it in, switching it on and observing the results. Then switch it off and unplug it before you approach it again. Be mindful that capacitors can keep a charge for minutes or even hours after power is applied. • Remember that with a metal chassis, the mains Earth must go straight to a chassis Earth point and then fan out from there, and that screw or bolt must not be used for any other purpose (eg, to hold a module to the chassis). This way, you will be able to happily and safely continue to build and work on electronics for many years. Subscription price reminder As mentioned in the August & September editorials, the cover price has now gone up by $1 (both AUD and NZD). The new subscription rates will take effect from the first of November, so there’s still time to get in at the old price if you want to. Cover Image: https://unsplash.com/photos/pAm8MHK0KqI Australia's electronics magazine by Nicholas Vinen siliconchip.com.au A BOM tool with brains — it’s our Forte Review lifecycles Forte The intelligent BOM tool® Authorized distributor of semiconductors and electronic components for design engineers. au.mouser.com/bomtool Save time MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Self-soldering PCBs? I came across the following video on self-soldering SMD circuits and thought it was an April Fool’s joke at first, but the video is very convincing. It has been around for six months or so; have you considered this type of thing for any of your projects? The limitations are around the solder temperature, board warpage and solder strength (as low-temperature solder is required). See https://youtu.be/ r0csHZveVvY Stephen Low, Brisbane, Qld. Comment: We have seen those videos. It is an interesting idea, but we don’t know how practical it is. For example, the PCBs required will be considerably more expensive (having at least four layers), and it will impose design limitations. Still, it is worth considering as an experiment. Note that you could easily reflow-solder standard PCBs if you build a DIY reflow oven (as described in our April & May 2020 issues at siliconchip.au/Series/343). Be aware that not all of our PCB designs are suitable for reflow soldering; you need an even distribution of copper over the PCB area so that all joints will reflow before any part of the PCB starts to burn. Keep that in mind if you plan to reflow a board that you haven’t designed. More on Oak vibrators My brother found one of the 50Hz vibrators that my father had made by Oak in the 1960s. These have the spring clip in the base. These were so the motor in a 12V-powered record player in the car would run at the correct speed. One thing I forgot to mention in my recent series of articles on vibrators (June-August 2023; siliconchip.au/ Series/400) is that if you have a 24V vibrator with separate switching contacts for the coil, you can disconnect the coil from that and connect it to a primary contact. Usually, it will still start on 12V, and with this configuration, the voltage to the coil gets boosted up to 24V by the transformer primary. It will then run normally, despite the 12V supply. Some vibrators were configured like this, without the separate coil contacts. You can also convert a 6V vibrator to run from 12V DC with that method. Dr Hugo Holden, Buddina, Qld. Reasons for Oak vibrator reliability In reference to John Reid’s comments on the Australian-­ made Oak vibrator (September 2023, Mailbag, page 6), there siliconchip.com.au are good reasons for its reliability. First, note that while the Oak V5105 shown was made in Australia, it was actually designed by the Oak Manufacturing Co in Chicago and patented in 1934. Around 1939, AWA began local manufacture of the vibrators under license to Oak. At first, the vibrators were branded AWA, but post-war, they were branded MSP (Manufacturers Special Products), along with various other AWA components. This was done to avoid commercial conflict, where competing manufacturers used AWA-made components in their sets. The secret to the reliability and long life of the Oak vibrator comes down to several design aspects. Importantly, Oak vibrators are of the ‘separate drive’ type. Most other vibrators are of the ‘shunt drive’ type, where the driving coil is switched by the same contacts that switch the transformer primary. In the separate drive type, the driving coil has its own contacts. This means that regardless of the condition of the primary switching contacts, whether oxidised or worn, the reed will always vibrate at its normal amplitude. To this end, Oak provided palladium-silver contacts for the drive coil, which avoided the problems of tarnishing. Furthermore, since the coil current is only about 200mA, these contacts have an easy life anyway. One of Oak’s patents was the short-circuited secondary winding on the driving coil, which was wound with resistance wire. The effect of this is to dampen the inductive spike when the contacts open, thus eliminating any sparking. Contrast all this to the shunt-drive vibrator, the most common type elsewhere in the world. Non-starting is common after years of disuse because the power contacts have built up a film of tungsten oxide or other film resulting from the rubber acoustic insulation decomposing. Even if the contacts are still clean, but the gap has increased due to wear, or just years of constant hammering, the driving coil action becomes erratic. In Australia, the competing vibrator manufacturer was Ferrocart, made by Astor. This is a shunt-drive design copied from the Utah Radio Products company, also from Chicago. Interestingly, it has smaller contacts: 3.96mm diameter vs Oak’s 4.32mm. Not surprisingly, this type of vibrator usually requires more work to get it going in the present day. However, even the best vibrator design will have a short life if the operating conditions are incorrect. Fortunately, in Australia, aside from Astor, most manufacturers used AWA’s Oak vibrator. Unlike in the USA, where Oak soon changed to the sealed, crimped can type of construction, AWA retained the spring clip to secure Australia's electronics magazine October 2023  5 the mechanism in the can, making servicing access very easy. This is, of course, much appreciated by restorers in the modern day. AWA further developed the Oak design, creating different voltage types that did not exist in the USA, and patented a split reed version. The type numbers were unique to Australian production, with few exceptions (such as the V5105 and V5124). Dr Holden’s US-made Oak V6295 is equivalent to the Australian V5948. Anyone wanting further information on Oak vibrators can refer to my website article www.cool386.com/msp/ msp.html Concerning Dr Holden’s mention of the Oak 50Hz vibrator, there was a shaver inverter article in Radio, Television & Hobbies, February 1960, in which an Oak vibrator was modified for 50Hz operation by applying solder to the reed weight. I understand that Bland Radio also used modified Oak vibrators to run 50Hz turntables for their DC radiograms. John Hunter, Hazelbrook, NSW. Editor’s note: we published a detailed article by John Hunter on vibrators in the December 2015 issue (siliconchip.au/ Article/9647). A better idea for a snuffer stick I read your advice to A.P. in Wodonga regarding a ‘snuffer stick’ in the July 2023 issue (Ask Silicon Chip, page 100). Your suggested two 220kW resistors to discharge a 22.5mF capacitor bank are inadequate. The RC time constant of the discharge circuit is about 10,000 seconds, close to 2.75 hours. Given that it will have discharged the caps to 1/e (~37%) of its original value of 600V in that time, it would still leave about 220V on the capacitors. Even after five and a half hours, there would still be over 80V on the caps. Three RC time constants is often quoted as the time to discharge a cap with a simple resistor, although five time constants are needed to ensure the cap is ‘fully’ discharged. I have worked in plasma physics for most of my working life, and we use much lower resistances to dump HV capacitor banks; for example, a 20W radiator element for a 450V 18mF bank (we had a lot of radiator bars and 450V caps back then). That would ensure that the bank voltage would be brought down rapidly, making the system safe in seconds in the event of some emergency. For servicing valve equipment, you’d want the voltage to come down to a safe level in 30 seconds to a minute (maximum), indicating a resistance of about 440W to 1kW. I’m too slack to work out a suitable power rating, but if the resistors are in some insulating tube, it is important to remember that will reduce their effective power rating. Having said that, if the discharge time is short enough, the resistors can be operated above their power ratings without problems, so long as the insulation doesn’t melt. If alligator or bulldog clips are to be used to connect the discharge resistor, they must be insulated, or the user will let fly some fruity language bound to scorch your grandmother’s ears! An important point for new users is that capacitors are prone to dielectric relaxation. After a capacitor has been charged to high voltage and then discharged, when the discharge path is removed, it will immediately start to recharge 6 Silicon Chip Australia's electronics magazine siliconchip.com.au itself! This process is often slow and may happen over hours, days or weeks, although it will start immediately. The eventual recharge voltage will depend on the original charge voltage, the time the capacitor has been charged and how long since the capacitor was discharged. Finally, a word on bleeder resistors that are permanently connected across HV capacitors. While they are not without merit (they should suppress dielectric relaxation), I have invariably found that the resistance required to discharge the caps in a reasonable time (like sometime before dinner) is usually too low for the circuit to tolerate, and the resistor will probably get intolerably hot. While one can always use a higher-powered resistor, the size is usually too big to be accommodated in the equipment. Phil Denniss, Darlington, NSW. Comments: You are right; a snuffer stick should comprise a much lower value resistance to reduce the capacitor voltage in seconds. If two in series 220W 5W resistors are used (for 440W ohms total) across the 22,500µF capacitance, the discharge for one time constant will be about 10s, and it should be reduced to a safe voltage in about one minute (six time constants). Inexpensive 50W resistors would handle the dissipation better although they are more bulky (eg, Rockby Cat 14239). The capacitor terminal voltage should always be measured before assuming it is safe to work on. A single Earth stake isn’t enough I thought your readers might benefit from the following comments. Until retirement, I spent my working life as an Electrical Protection Engineer, so I couldn’t sit back in silence. In the letter titled “More on Solar Powered Sheds,” on page 11 of the of the August issue, Rick Arden states that he has Earthed the shed to the correct standard using a long copper-coated rod. Unless that rod is of sufficient length and is connected to the MEN scheme, it would not meet AS3000 as I understand it. The purpose of an Earth electrode is to provide a sufficiently low resistance to Earth so enough Earth fault current can flow to blow the switchboard fuse or trip the switchboard circuit breaker, isolating the faulted circuit or device from its supply. The Earth resistance of a single copper-clad rod will almost certainly be far too high to accomplish this purpose. Although I have performed Earth tests in several Australian states, I have yet to find a standalone Earth rod that meets that requirement because soil resistance is simply too high. The rod needs to be connected to a multitude of well-­ separated rods, which is usually achieved by using the multiple-­ Earthed neutral (MEN) scheme. In the MEN scheme, the Earth rod at any single premises is connected to the Neutral conductor, which runs along the street and is connected to all the Earth rods in the neighbourhood. Thus, all the rods are connected in parallel, providing a sufficiently low Earth resistance. In addition, there must be a return path, and that is provided by the distribution transformer neutral Earth, which is more extensive and has quite a low Earth resistance. Rick’s electrical arrangement diagram shows that the Earth rod is connected to the inverter enclosure. If so, it would provide no return path for Earth currents flowing 8 Silicon Chip from faulty equipment plugged into the inverter. If it is connected to a Neutral in the inverter, it will almost certainly not allow sufficient current to flow to trip the supply unless some sort of Earth leakage protection exists. Responding to such low currents flowing via the Earthing rod will require an Earth Leakage Circuit Breaker, otherwise known as an RCD (residual current device). Per the much-celebrated Murphy’s law, a single rod will have been driven into the ground in a location with unusually high soil resistance. Though unlikely, it is conceivable that insufficient current will flow to trip an RCD. This is an important consideration because, as purchased, most RCDs are set to trip at a current well above the sustained lethal hand-to-foot or hand-to-hand current. Their saving grace is the speed with which they operate. Finally, I should point out that installing multiple Earth rods in close proximity is an exercise in diminishing returns. Each rod will ‘shade’ those nearby and reduce their effectiveness. Anything less than a separation of about four times their length is ill-advised. You might also be surprised to learn that dampness doesn’t always have much effect in lowering the Earth resistance. Any soil bereft of minerals will return a high soil resistivity and provide a poor Earth regardless of moisture content. For example, whereas the Dandenong Ranges outside Melbourne have very fertile soil and higher rainfall than Melbourne, the lack of minerals and the shallowness of soil above the bedrock there makes obtaining a good Earth comparatively vexatious. This is also true of areas subject to high tropical rainfall, as the rain leaches the minerals from the soil over the long term. Ron, East Oakleigh, Vic. Watch out for incorrect electricity charges Everyone now has concerns about electricity costs and realises that it is important to minimise costs. I updated my battery storage system from Alpha S5 to Tesla Powerwall 2 because the former exported large amounts of energy even if the battery was less than a third charged. If the load exceeded about 2kW for a 4.6kW inverter, it went into fault mode and did not restart as it should. The replacement Tesla Powerwall 2 is very versatile and efficient in storing all available energy from the solar panels. It can also charge from the grid as needed or store offpeak energy for use in peak tariff mode. That is useful in winter when there is low solar energy available. Now that I was so happy with my battery, I checked my bills and energy usage against the peak time of 3pm to 9pm each day. However, I discovered that the smart meter recorded my usage as being at peak rates between 7am and 11pm on weekdays! I confirmed that this was how I was being billed (based on what the smart meter reported). I notified my retailer of this, and they resolved it. It was found to be due to a plan data error that has now been fixed for me and others. They were thankful for my pointing out the problem they did not know about. They also fixed a problem where I was being charged using estimated readings for my smart meter. It was found to have been caused by a faulty comms card (Mesh card) in mine and a few other people’s meters. Australia's electronics magazine siliconchip.com.au Keep your electronics safe with our HUGE RANGE of Low Voltage Circuit Protection SAME GREAT RANGE AT SAME GREAT PRICE. ESPECIALLY HANDY IN A BOAT OR CARAVAN WHICH MAY NOT HAVE A CHASSIS GROUND TYPE SYSTEM CONTROL LIGHTING AND OTHER 12V GEAR AROUND THE BOAT & VEHICLE Blade Fuse Blocks with Bus Bar • Suits standard blade fuses • 30A per output, 100A combined • Red LED blown fuse indication • Negative bus bar 6 Way SZ2031 | 12 Way SZ2032 FROM 3895 $ PERFECT FOR HIGH END CAR AUDIO SYSTEMS, SOLAR INSTALLS AND OTHER HIGH CURRENT 12V APPLICATIONS Heavy Duty Circuit Breakers • Visible Trip / Circuit Breaker Button • Switchable / Manual Push-To-Trip Operation • Multi-wire gauge inputs and outputs 60A SZ2081 | 120A SZ2083 | 200A SZ2085 • 10A rated illuminated rocker switches • Push-to-reset 10A, 8A, 6A and 4A circuit breakers • Negative bus bar • Mount vertically or horizontally 4 Way SZ1902 6 Way SZ1903 JUST 59 $ Marine Switch Panels with Circuit Breakers FROM 4495 $ 95 EA Here's a small selection of our Fuses and Holders See our HUGE RANGE in-store or online SEE OUR STAFF IN-STORE FOR THE FUSE OR CIRCUIT BREAKER TO SUIT YOUR APPLICATION ANL In-line Fuse Holder • Suits ANL Wafer Fuses • Nickel plated • Protective cover SZ2078 JUST 22 $ 95 Gold ANL Wafer Fuses • 80A, 100A, 150A, 200A & 250A models • Screw down contacts SF1990-SF1999 JUST 9EA $ 95 Automotive Fuse Assortment • 20 x 5A, 10A, 15A, 20A, 25A & 30A ATO size fuses included • 120 pieces with storage case SF2142 JUST 2995 $ Shop at Jaycar for Mains Voltage Circuit Protection: • Surge Arrestors • Transient Voltage Suppressors • Fuses and Fuse Holders • MOV & Noise Suppressors • PTC Fuses • Thermal Fuses and Switches Explore our full range of circuit protection products, in stock at over 110 stores or 130 resellers or on our website. siliconchip.com.au Australia's electronics magazine jaycar.com.au/circuitprotection 1800 022 888 2023  9 October Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. So I remind everyone to check their electricity bills properly, especially if they have a smart meter. By the way, the story on the Reciprocal Frequency Counter was great (July 2023; siliconchip.au/Article/15863). We used a Hewlett-Packard version of the same device some 30 years ago. Wolf-Dieter Kuenne, Bayswater, Vic. Early radio pioneers ID-50A VHF / UHF DUAL BAND DIGITAL TRANSCEIVER ® IPX7 Since 1964 10 Silicon Chip To enrich the excellent article “100 Years of Broadcast Radio”, written by Mr Kevin Poulter and published in the last edition of Silicon Chip (siliconchip.au/Article/15939), I pose a question for reflection: was Marconi really the inventor of the radio? According to numerous sources*, the first successful wireless transmission and reception experiments with audio were carried out by Father Roberto Landell de Moura in 1894, before Guglielmo Marconi. However, at that time, he had to deal with the ignorance of the authorities, the lack of resources, the challenge of showing that the church was not an enemy of science and not being part of the scientific community. As a result, his work did not get the recognition it deserved, and he was virtually unknown outside Brazil. In 2011, the Brazilian Post Office issued stamps commemorating 150 years since his birth. Dr Marco Feris, Shellharbour, NSW. Kevin Poulter responds: I could nominate several other early inventors of radio. However, Marconi was the inventor who transmitted voice a great distance, constantly promoted broadcasting worldwide, made radio a practical, widely-available device, and even profited the most. Similarly, Edison did not invent the light globe but made and continued to make longer-lasting globes. The first ones had a life of only a few hours or less. Swan in the UK was also developing light globes but did not patent all of them, as he said everyone was making them. So much so, it was not hard to find scientific journals and magazines that illustrated the construction details. When Edison found no patent in the UK for his more successful globe, he took one out and negotiated with poor Swan to be a partner. That was the start of the Ediswan brand that lasted a long time. Edison was a genius businessman, with over a thousand patents to his name (although Swan himself had over 70). Edison’s main genius was marketing and strategically applying for patents. Plus, he had a workshop with as many as 200 men working in the six-building lab complex. Half of his 1093 patents came to light there. When something was invented, Edison’s name went on it. That really annoyed Tesla, so he left. Editor’s note: this discussion is well-timed as we have a three-part article series starting in this issue (just after this column) on early electronic inventions. Reading it, one theme that becomes apparent is how many people contributed to each invention and how much controversy there was over who came up with an idea first, especially in the early days. I also refer readers to our two-part article on Edison (September & October 2006; siliconchip.au/Series/79) by Kevin Poulter. * For details on de Moura, you can visit siliconchip.au/ link/abpp and siliconchip.au/link/abpq SC Australia's electronics magazine siliconchip.com.au Rack Equipment Ideal for IT Networking, Small Offices, Recording Studios, Sound & PA Equipment. GREAT VALUE and IN STOCK at your conveniently located stores nationwide. 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Jaycar reserves the right to change prices if and when required. FROM 139 $ ELECTRONICS Inventors and their Inventions invented the same thing; those who get the most credit were not necessarily the original discoverers. Also, many inventions represent the culmination of the work of many people. Some inventions are not necessarily the result of the labours of any specific individual but result from many contributions. We have tried to be as comprehensive as possible, but there will be inventions or inventors we have not been able to include in the available space. This series contains three parts. This first part, and the follow-up next month, will detail various individual inventors, usually with multiple inventions over a range of dates, organised by their birth dates. The third and final part will mostly cover inventions attributed to a company or other organisation, such as a university. We have endeavoured to use multiple sources to find accurate dates; dates often vary between sources, sometimes significantly. Here is our list of inventors by date of birth (up to 1847): Thales of Miletus static electricity Who laid the groundwork for modern technology? Modern inventions like transistors, ICs and wireless communications didn’t come out of thin air; thousands of brilliant scientists and inventors had to discover every aspect of the electronic technology that made them possible over the last few hundred years. Part 1: by Dr David Maddison O ver the last few years, we have examined many aspects of modern electronics history, such as transistors, batteries, IC fabrication, display technologies and computer memory (see the panel below). However, those articles don’t tell the full story because of how many important discoveries had to be made before any of that was possible. We will look at the people behind those discoveries in this series of articles. The inventors and inventions described herein form the basis of all modern electronics. You may be surprised, as we were, at how early some advanced concepts were conceived. Many modern devices were invented way ahead of their time. 12 Silicon Chip https://unsplash.com/photos/_kdTyfnUFAc They often failed to find a use then, only to become very popular later. Many of the scientists and engineers described below contributed far more than we can describe in the space available. It was common to be a polymath (multi-disciplined) ‘back in the day’. We will focus on those areas of discovery and invention most relevant to electricity and electronics. Note that many people independently c.624BCE-c.546BCE Described the generation of static electricity by rubbing amber, which caused it to attract feathers and other light materials. He also observed that lodestone, a form of magnetite naturally magnetised by lighting, could attract iron. Theophrastus pyroelectricity c.371BCE-c.287BCE Is said to have discovered pyroelectricity, the property of a material to temporarily become charged when heated and attract light materials like ash, similar to when amber is rubbed. William Gilbert 1544-1603 electricity Coined the term “electricus”, from which the word electricity is derived. He also explained that compasses worked because the Earth is a giant magnet with an iron core. He wrote a book in 1600 with the title “De Magnete”. You can read that book at www. gutenberg.org/ebooks/33810 He also invented the instrument Other recent articles on the development of electronics All About Batteries, January–March 2022; siliconchip.au/Series/375 The History of Transistors, March–May 2022; siliconchip.au/Series/378 IC Fabrication, June & July 2022; siliconchip.au/Series/382 Display Technologies, September & October 2022; siliconchip.au/Series/387 Computer Memory, January & February 2023; siliconchip.au/Series/393 Australia's electronics magazine siliconchip.com.au Fig.1: Ebenezer Kinnersley’s ‘Electrical FIRE’ lecture notice. Source: Brown University Library (https:// library.brown.edu/dps/ curio/2013/05/). now known as the electroscope, which detects the presence of electric charge. Gilbert mistakenly did not believe electricity and magnetism were related; Hans Christian Ørsted and James Clerk Maxwell later showed them to be. Otto von Guericke electrostatic generator 1602-1686 He invented the first electrostatic generator, a sulfur sphere that could be rubbed to impart an electric charge to attract or repel objects. It inspired other, more advanced frictional generators. Christiaan Huygens wave theory of light 1629-1695 Developed the wave theory of light in 1690, which related to electric and magnetic fields. Francis Hauksbee the Elder modified electrostatic generator 1660-1713 Made a modified version of Otto von Guericke’s electrostatic generator in 1705, a partially evacuated glass sphere into which mercury was introduced. If rubbed to generate a charge, a glow was produced where the glass was touched. This led to the much later development of the gas discharge lamp, neon lighting and mercury vapour lamps. You can read his book “Physico-­ discoveries, but today, some know him mechanical experiments” at https:// as the “father of electricity”. catalogue.nla.gov.au/catalog/3171279 Pieter van Musschenbroek 1692-1761 Johann George Schmidt pyroelectricity unknown Observed in 1707 that the mineral tourmaline had a property we now know as pyroelectricity. Stephen Gray electrical conductivity 1666-1736 Discovered the principles of electrical conductivity and distinguished between conductors and insulators. He also made discoveries in electrical induction, imparting a charge into another object without contact. He received little credit for his Christiaan Huygens also invented the pendulum clock. Source: https://w. wiki/7ATc siliconchip.com.au Leyden jar / capacitor Along with his student and a collaborator, he invented what became known as the Leyden jar in 1756, the original capacitor. It was used to store electrical energy produced by frictional generators. It consisted of a glass jar filled with water, a brass rod and another conductor. You can easily make a Leyden jar; see the video from ElectroBOOM at https://youtu.be/xjW-isgOijs and www. wikihow.com/Make-a-Leyden-Jar Ewald Georg von Kleist Kleistian jar 1700-1748 Invented the Kleistian jar in 1745, a form of Leyden jar. Benjamin Franklin lightning rods, glass harmonic etc 1706-1790 He named positive and negative charges in 1747. In 1748, he constructed a multi-plate capacitor with glass and lead plates. In that same year, he invented the “electric wheel”, a type of electrostatic motor that would run at 12-15RPM from a charge supplied by Leyden jars. In 1750, he showed that Leyden jars Australia's electronics magazine Fig.2: Kinnersley’s “electric air thermometer” used a spark discharge to push water up a tube. Source: https://w.wiki/78sQ discharged more easily near a pointed rod, leading to the invention of lightning rods (also see Kinnersley’s entry). In 1752, he flew a kite in a thunderstorm to charge a Leyden jar attached to the wet string, proving that lightning was electricity. (The following two people who tried that were electrocuted.) In 1751, he published a series of pamphlets on electricity (siliconchip. au/link/abnr). Carl Linnaeus 1707-1778 pyroelectricity Determined that pyroelectricity was a type of electricity in 1747. He later became known as Carl von Linné after being ennobled Ebenezer Kinnersley electric fire / electricity 1711-1778 Performed experiments with “electric fire”, as electricity was then called – see Fig.1. Benjamin Franklin described him as “an ingenious neighbor”. In 1748, he discovered that electricity passed through water. In 1751-2, he held a series of lectures about electric fire. In his March 1752 lecture, he suggested the lightning rod to protect structures from lightning before October 2023  13 Benjamin Franklin was one of the Founding Fathers of the USA. Source: https://w. wiki/7ATw by Benjamin Franklin in 1748. It was incapable of useful work, but some call it the first electric motor. It consisted of a free-spinning star with angled, pointed ends that were charged from a power source. Ionised gas from the tips caused it to rotate. For more details, see siliconchip.au/ link/abn2 Franz Aepinus electricity and magnetism 1724-1802 He was the first to publish a treatise on electricity and magnetism (see his book at: siliconchip.au/link/abnu). Johan Carl Wilcke electrophorus Franklin did his kite experiment. In 1761, he wrote a letter to Franklin and, in 1763, published details of an “electric air thermometer” – see Fig.2. He demonstrated that electricity could produce heat. In 1761, he used electricity from Leyden jars to heat metals to incandescence, producing visible light, paving the way for the light globe. See “Expt. 11” in his letter to Franklin (siliconchip.au/link/ abp2). You can find instructions to make a “proof of concept” light globe on Hackaday: siliconchip.au/link/abnk 1732-1796 Invented the electrophorus, a device to produce static electricity, in 1762. Luigi Galvani bio-electricity 1737-1798 He is famous for discovering that frog’s legs will twitch with the application of an electric discharge from a charged Leyden jar. He also made the legs move with two differing metals that generated a current like a battery. Due to this early work in the field of bioelectricity, many modern electrical-­related phenomena are named after Galvani. Charles Coulomb Coulomb’s law / electric charge 1737-1806 to the magnitude of their electric charge and the inverse square of the distance between them. This was known earlier, but it is named after Coulomb, as he was the first to publish it in 1785. The Coulomb (C) is also the unit of electric charge. Alessandro Volta 1745-1827 battery (voltaic pile) He improved the electrophorus in 1775. Then in 1800, he invented what is now known as the voltaic pile or battery made of copper and zinc, using either saltwater or sulfuric acid electrolyte. He acknowledged the contributions of William Nicholson, Tiberius Cavallo and Abraham Bennet to his battery work. The unit of electrical potential, the volt (V), was named in his honour. He discovered by accident that a short circuit of his voltaic pile caused a copper wire to glow, confirming the principle of the incandescent light globe. Pierre-Simon Laplace Laplace transform Developed the Laplace transform in 1785. It is used to solve differential equations, making it essential for circuit analysis. Vasily Vladimirovich Petrov electric arc – welding Invented the “electrical whirl” (Fig.3), described in 1745 (siliconchip. au/link/abnt). It was an electrostatic reaction motor, also demonstrated Invented the torsion balance, which enabled him to measure forces of attraction or repulsion between charged or magnetised bodies. Coulomb’s law states that the force between two electrically charged bodies is proportional Fig.3: an electric whirl similar to the one invented by Andrew Gordon in 1745. This one is on display in the physics department of Washington and Lee University. Source: http:// physics.kenyon.edu/EarlyApparatus/ Static_Electricity/Electric_Whirl/ Electric_Whirl.html Fig.4: Wollaston’s improved battery with removable electrodes. Source: https://w.wiki/78sR Andrew Gordon electrostatic reaction motor 14 Silicon Chip 1712-1751 Australia's electronics magazine 1749-1827 1761-1834 Discovered the electric arc in 1802 after he built the world’s largest voltaic pile, comprising 4200 copper and zinc discs. In 1803, he proposed several uses for the electric arc, such as lighting, welding, metal processing etc. siliconchip.com.au Fig.5: an 1878 reproduction of one of Davy’s original arch lamps by Augustin Privat Deschanel. Source: https://w.wiki/78sS William Hyde Wollaston 1766-1828 static electricity and electromagnetic induction Demonstrated that static electricity was the same as from voltaic piles in 1801. He was said to have “accidentally” discovered electromagnetic induction 10 years before Faraday (who made the discovery in 1831) and made a failed attempt to build an electric motor. He built an improved type of copper/zinc battery in which the electrodes were raised from the electrolyte when not in use, improving the life – see Fig.4. John Dalton atomic theory – materials 1766-1844 Contributed to atomic theory in ways that improved the understanding of conductors, insulators and semiconductors. Thomas Johann Seebeck thermocouples / thermopiles 1770-1831 Discovered in 1822 that a junction of two dissimilar metals produced a current. This is the basis of thermocouples, used to measure temperature, and thermopiles, which convert heat into electricity (such as radioisotope thermoelectric generators on spacecraft). Thomas Young expanded on wave theory 1773-1829 He expanded on the wave theory of light (first described by Huygens), vision and colour theory. André-Marie Ampère Amperè’s force law and solenoid 1775-1836 Set out to discover the relationship between electricity and magnetism. In 1820, Ampère’s friend, Dominique François Jean Arago, demonstrated the discovery of Hans Christian Ørsted that a current-carrying wire deflects a magnetised needle. Ampère determined that two parallel current-carrying wires would either attract or repel each other depending on the relative current directions and established Ampère’s force law. He invented the solenoid and had an idea for an electric telegraph. The SI unit for electric current, the amp (A), is named after him. Inspired by Ørsted, he also established Ampère’s righthand grip rule. Carl Friedrich Gauss ionosphere and electric telegraph 1777-1855 Popularised Gauss’ law in 1813, although it had already been discovered by Joseph Louis Lagrange in 1762. In 1839, he postulated that an electrically conducting region of the atmosphere, now known as the ionosphere, siliconchip.com.au reflected radio waves. The unit of magnetic induction, the gauss (G), is named after him. He had achievements in many other areas. He worked with Wilhelm Eduard Weber to develop an electric telegraph in 1833. Hans Christian Ørsted 1777-1851 Oersted’s law and right-hand thumb rule Discovered in 1820 that the needle of a compass would deflect near a current-­carrying wire, establishing that an electric current had a magnetic field, the first connection between electricity and magnetism. He established Oersted’s (or Ørsted’s) law which states that an electric current establishes a magnetic field around it. That led to the “right-hand thumb rule”, which describes the relationship between a current and its magnetic field. A unit of magnetic field strength, the oersted (Oe), is named after him. Sir Humphry Davy 1st Baronet carbon arch lamp 1778-1829 Invented the carbon arch lamp, later renamed from arch to arc (see Fig.5), in 1802, 1805, 1807 or 1809 (depending on the source). He used charcoal sticks and a 2000-cell battery to strike an arc across a 100mm gap. The electrodes were originally horizontal, and the arc was shaped like an arch, hence the name. Arc lamps were widely used for street and commercial lighting from the 1870s until they were replaced by incandescent lighting from the early 1900s (except for specific applications like searchlights and movie projectors). Movie reels used to commonly be 2000ft (610m) long, with a runtime of about 22 minutes. That coincided with the life of carbon rods in pre-1970s theatre projectors. The projectionist would change the carbon rods at the same time as the reel. In 1801 or 1802, Davy also connected Australia's electronics magazine a piece of platinum across a 2000-cell battery, which caused it to glow, the basis for later experiments in incandescent lighting. Michael Faraday was Davy’s assistant from 1813 to about 1815, and occasionally helped him after that, such as with the Miner’s Safety Lamp. William Sturgeon electromagnet 1783-1850 Invented the electromagnet in 1824 – see Fig.6. It comprised 18 turns of copper wire on a lacquered iron U-shaped core, 30cm long and with a 13mm diameter. It was powered by a copper-zinc-acid battery. The cups contain mercury to make electrical connections. The magnet could support 4kg. Samuel Hunter Christie 1784-1865 “diamond method” (Wheatstone Bridge) Published the “diamond method” to compare resistances in 1833, a forerunner of the Wheatstone Bridge. Baron Pavel Schilling Schilling telegraph 1786-1837 Made numerous contributions to telegraphy and other areas. One of those inventions was the Schilling Fig.6: William Sturgeon’s electromagnet. Source: https:// w.wiki/78sT October 2023  15 telegraph, a type of ‘needle telegraph’ that sent a code along a series of wires to indicate the letter according to a binary code. His first telegraph was shown in 1828. It used only two wires with an innovative variable-length binary code to encode 40 letters. The current direction also varied, so two wires could give eight different states. He demonstrated another instrument with six wires in 1832. To transmit 40 different characters, six wires were needed for signalling, one for calling and one for a return. He abandoned the project because, from 1825, Czar Nicholas I of Russia opposed any form of mass communication and prohibited the public discussion of telegraphy. Dominique Fançois Jean Arago 1786-1853 eddy currents Conducted experiments with magnetism, mostly in 1823-1826. In 1824, he observed “rotary currents” or eddy currents. “Arago’s rotations” demonstrated interactions between a spinning non-magnetic conductor such as a copper disc and a magnetised body like a compass needle or magnet. Sir Francis Ronalds electric telegraph 1788-1873 Produced the first working electric telegraph in 1816. It was not until two decades later that commercialisation happened. V² V ΩA² Ω Ω VA ΩW W A W V W A V Ω V² W W ΩA A² W Ω V A Fig.7: an Ohm’s Law wheel calculator. Source: https://w.wiki/78sV (CCSA-3.0). In it, he detailed his theory of electricity, including the concept of resistance and what is now known as Ohm’s law – see Fig.7. In 1825, he used different lengths of wire (10cm, 41cm, 183cm, 315cm and 762cm) to produce different resistances, deriving Ohm’s law. It might be argued that he invented the resistor, although the concept of resistance was already known at the time. The unit ohm (Ω) is named after him. Michael Faraday electromagnetic induction 1791-1867 Published “The Galvanic Circuit Investigated Mathematically” in 1827 – see siliconchip.au/link/abp3 Built a device to produce continuous “electromagnetic rotation”, now called the homopolar motor (Figs.8 & 9) in 1821, soon after Ørsted discovered electromagnetism. Faraday had discussed such a device with Sir Humphry Davy and William Hyde Wollaston, but failed to acknowledge them as contributing Michael Faraday holding what is most likely ferromagnetic material. Source: https://w.wiki/7AUi Fig.8: two versions of a magnetic rotation apparatus, the first motor. On the left, the lower magnetic rod rotates about the centre, while on the right, the upper wire rotates about the centre magnet. The liquid is mercury. Source: Michael Faraday. Georg Simon Ohm Ohm’s law 16 Silicon Chip 1789-1854 Australia's electronics magazine to his invention, causing controversy. See: siliconchip.au/link/abn4 In 1831, Faraday discovered electromagnetic induction, demonstrating that a change in the magnetic field within a circuit induces an electromotive force (EMF) – see Fig.10. This discovery is the basis for electric power generation and led to the invention of the electrical generator and transformer. Joseph Henry independently discovered it in 1832, but Faraday published it first. In 1833, he published “Faraday’s laws of electrolysis”, introducing terms such as electrode, anode, cathode, electrolyte and ion. He observed that the resistance of silver sulfide decreased as its temperature increased, the first mention of what we now call a thermistor, a semiconductor with a strongly temperature-­dependent resistance. This was also the first observation of a semiconductor. The unit of capacitance, the farad (F), is named after him. Faraday also made numerous contributions in other areas; his theoretical work on the nature of the electromagnetic field led to the development of field theory in physics. Samuel Morse Morse Code 1791-1872 Developed the concept of the single-­ wire telegraph and invented Morse Code in 1840 (later enhanced by Alfred Lewis Vail). In developing the telegraph, Morse had a problem of limited range, which he solved with the help of Professor Leonard Gale, by adding relay circuits. Fig.9: a simple homopolar motor you can make with a battery, a length of wire, a neodymium magnet and a steel screw. Source: https://w. wiki/78sX (CC-BY-SA-2.5). siliconchip.com.au + − Fig.10: an iron ring apparatus used by Faraday to observe electromagnetic induction. Momentarily completing the circuit on the left resulted in a momentary current on the right. Source: https://w.wiki/78sW Morse was contracted to build a 61km telegraph line between Washington, DC and Baltimore in 1843, which opened in 1844, with the first words transmitted being “What hath God wrought”. By 1850, 19,300km of telegraph lines had been laid across the USA. Morse’s 1840 telegraph patent can be seen at siliconchip.au/ link/abn6 The Morse Code standard today (still in use by some radio hams) is defined by ITU-R M.1677-1 and is based upon the work of Friedrich Gerke in 1848, which led to the International Morse Code of 1865. electrolysis. The hydrogen and oxygen produced were used in a form of stage lighting called limelight. The generator was also used for electric arc lighting and galvanising. The AC generated by the machine was converted to DC by a commutator. Johann Poggendorff slide wire potentiometer 1796-1877 Invented the slide wire potentiometer (variable resistor) in 1841. Around 1870, he also developed an electrostatic motor. Joseph Henry 1799-1878 electromagnet and mutual inductance Fig.11: Joseph Henry’s “intensity magnet”. Source: https://w.wiki/78sY motor based on a rocking rather than rotary motion (see Fig.12). The unit of inductance, the henry (H), is named after him; it is thought that Henry discovered inductance before Faraday, but Faraday published his findings first. Patented a magneto generator in 1850 for decomposing water by Improved upon Sturgeon’s electromagnet of 1824, in 1827, by using tightly wrapped silk-insulated wire rather than the uninsulated wire of Sturgeon – see Fig.11. This allowed Henry to use many layers of wire to make a more powerful magnet. He also discovered self-­ induction and mutual inductance. In 1831, he made the world’s first commercial electrical product, a powerful electromagnet to separate magnetite from crushed ore (see the video at https://youtu.be/ru-daEOuUjs). Also in 1831, he developed the first electric Joseph Henry in 1879. Source: https://w.wiki/7AU$ Fig.12: Joseph Henry’s rocking beam electric motor of 1831. It pivoted in the middle with its ends in line with permanent magnets (C and D). As it rocked, electrodes contacted batteries at the ends (G and F), the magnet polarity reversed, and the beam would rock the other way. Source: https://siarchives. si.edu/collections/siris_sic_13161 Marcellin Jobard incandescent lighting 1792-1861 Suggested incandescent lighting in 1838, quoting É.M. Alglave and J. Boulard, “a small strip of carbon in a vacuum used as a conductor of a current, would emit an intense, fixed, and durable light”. His student, CharlesFrançois de Changy, commenced work on the idea in 1844. Floris Nollet magneto generator siliconchip.com.au 1794-1853 Australia's electronics magazine Nicholas Joseph Callan induction coil and Maynooth battery 1799-1864 Invented the induction coil in 1836. It is a form of transformer driven by a pulsating direct current at about 20Hz using an “interrupter” to make and break the current flow. Despite not inventing it, Heinrich Daniel Ruhmkorff patented it in 1951 and then commercialised it. In 1848, he also commercialised the world’s largest battery at the time, the October 2023  17 Fig.13: the Maynooth battery. At the back is the zinc plate; in front of it is a porous ceramic pot. Both are inside the iron container, which forms the other plate. Source: Maynooth College Museum – siliconchip. au/link/ abp7 “Maynooth battery” (Fig.13) from iron and zinc, with 136L of acid and 577 individual cells. Back then, there was no way to measure voltage or current, so he measured the lifting capacity of an electromagnet to test its relative power. James Bowman Lindsay incandescent light globe 1799-1862 Invented the first incandescent light globe in 1835, enabling him to “read a book at the distance of 1½ foot”, but he never patented it and did not receive credit. In 1845, he suggested that telegraphy could work across water, including the Atlantic. He proposed welding to join the cables and sacrificial anodes for corrosion protection. Frederick Collier Bakewell fax machine 1800-1869 Demonstrated an “image telegraph” machine in 1851, an early fax machine and an improvement upon the system of Alexander Bain. The system worked by drawing on metal foil using insulating ink. The foil was rolled into a cylinder, and a stylus read the conducting and insulating areas, converting them into signals to be transmitted. The image was reconstructed on treated paper that electrical impulses could discolour. Keeping appropriate synchronisation at both ends was difficult, and the system was never commercialised. Moritz Hermann Jacobi’s law Fig.14: Jean-Daniel Colladon’s experiment demonstrating total internal reflection in a stream of water. Source: La Nature magazine, 1884. Also known as Boris Semyonovich (von) Jacobi, invented a process for making printing plates by electroplating in 1838. In 1839, he made an 8.5m-long battery-powered boat that carried 14 passengers. He studied electric motors and, in 1840, published the maximum power theorem or Jacobi’s law, which states that for maximum power transfer, the load resistance must match the source resistance. He also worked on the development of the electric telegraph during 1842-1845. Charles Wheatstone telegraph and Wheatstone bridge Fig.15: a replica of Weber’s electrodynamometer made in 1961. Source: https:// americanhistory. si.edu/collections/ search/object/ nmah_1273644 18 Silicon Chip 1801-1874 1802-1875 He performed an experiment in 1834 to determine the “velocity of electricity”. His result was about 50% too high. In 1837, Wheatstone also began work with William Fothergill Cooke on the telegraph. In 1843, he improved and popularised Samuel Hunter Christie’s “diamond method”, which became known as the Wheatstone Bridge. Australia's electronics magazine Jean-Daniel Colladon total internal reflection (TIR) 1802-1893 Demonstrated total internal reflection in a falling stream of water in 1842 (an experiment which can be done at home) – see Fig.14. This allowed optical fibres to be developed much later. The original idea was used to illuminate water fountains such as at the Paris World Exposition of 1889. Frederick de Moleyns 1804-1854 platinum filament incandescent light globe He obtained the first patent for an incandescent light globe in 1841. It used a platinum filament, although he also experimented with carbon filaments. Emil Lenz 1804-1865 Lenz’s law, resistive heating and electroplating Formulated Lenz’s law in 1834, which specifies the direction of a current induced by a magnetic field. He also independently discovered Joule’s law (or the Joules-Lenz law) in 1842, which describes how an electric current causes a conductor to heat, otherwise known as resistive or ohmic heating. He also participated in the development of electroplating with his friend Moritz Hermann. Louis Breguet 1804-1883 Foy-Breguet telegraph Developed a needle telegraph in 1842, the Foy-Breguet telegraph, used on the French railways and in Japan. In 1847, he suggested using finer diameter wires to protect telegraph wires against lightning strikes, the predecessor of the fuse. Wilhelm Eduard Weber electrodynamometer 1804-1891 Together with Carl Gauss, he built the first working electric telegraph, nearly 1.6km long, in 1831. Weber developed many sensitive devices for detecting and measuring electric currents and magnetic fields, including precise measurements of the Earth’s magnetic field. He also invented the electrodynamometer (Fig.15), a device that can measure current, voltage or power via the interaction of magnetic fields through two coils. This device was used to validate Ampère’s force law experimentally. The SI unit of magnetic flux, the weber (Wb), is named after him. For more on Weber, visit: siliconchip.au/link/abn7 Robert Davidson electric train 1804-1894 Built the first electric locomotive in 1837, which was powered by galvanic siliconchip.com.au cells. He then built a full-sized train in 1842 called “Galvani”; it was around 5m long. Edward Davy electric relay 1806-1885 He worked on the electric telegraph during 1835-1838 and was considered a contributor equal to Cooke and Wheatstone by J.J. Fahie. In 1837, he invented the electric relay, or “electric renewer” as he called it, as part of his telegraph system. In 1838, he migrated to Australia. Duchenne de Boulogne electrophysiology 1806-1875 Experimented with electrical stimulation on parts of the human body and is considered a pioneer in electrophysiology. He first published his work, “De l’electrisation localisée...” in 1855. You can read that book in the original French at siliconchip.au/link/abn8 Alfred Lewis Vail improved on Morse Code 1807-1859 Was involved with Samuel Morse in commercialising telegraphy 18371844. He enhanced Morse Code by simplifying the alphabetic system, making it easier to decode, along with other physical improvements. Antonio Meucci telephony and dynamic microphone 1808-1889 According to some, he was the inventor of telephony. His notes show he produced a device in 1856 that The invention of electric light The story of the invention of electric light is far too long and complicated to fully cover here. We have included highlights, but if you want to know more, read “The Invention of the Electric Light” (236 pages) by B.J.G. van der Kooij, a free PDF download from siliconchip.au/link/abnh communicated voice via wires from his basement laboratory to his wife upstairs in their New York home. This included a type of dynamic microphone with a wire coil moving in response to sound within a magnetic field. From 1856 to 1870, he developed more than 30 types of phone apparatus. In 1860, he publicly demonstrated his “teletrofono” in New York. In 1870, he transmitted voice signals over more than 1.6km of wire. In 1871, he submitted a patent caveat to the US Patent Office. This document was essentially a notice of an intent to file a patent, but Meucci didn’t have the money to submit a patent application. Had he been able to, it might have stopped Alexander Graham Bell from receiving his telephone patent in 1876. Hippolyte Pixii 1808-1835 hand-cranked dynamo (electrical generator) Invented a hand-cranked dynamo in 1832 based on Michael Faraday’s discovery of electromagnetic induction. It produced an alternating current when a horseshoe (permanent) Fig.16: Pixii’s dynamo. This later version produces pulsating direct current using the commutator below the magnet. Source: https://w. wiki/78sZ siliconchip.com.au magnet passed over two iron cores – see Fig.16. At the time, DC was the preferred means of current for experiments. Upon André-Marie Ampère’s suggestion, a commutator to reverse the current direction every half turn was later added to produce pulsating direct current. William George Armstrong hydroelectric power station 1810-1900 He built the first hydroelectric power station (Fig.17) in 1870. It was the Burnfoot Power House at Cragside Estate, Rothbury, England and used a Siemens dynamo. He was titled 1st Baron Armstrong. Alexander Bain electric clock and facsimile machine 1810-1877 Patented an electric clock in 1841 with John Barwise. Its pendulum was driven by electromagnetic pulses. It included a reference to an “earth battery” made of dissimilar metals, buried in the ground, as a power source. He also patented a telegraph in 1843 that printed messages, an early form of the facsimile machine. The image to be Fig.17: the first hydroelectric power station, on a private estate in Rothbury, England. Source: https://w.wiki/78sa (CC-BY-SA-4.0). Australia's electronics magazine October 2023  19 Controversy over the invention of the telephone You may have noticed many references to various people who made telephone-­ related inventions. The matter of who invented the telephone has been subject to considerable controversy, including the long-running court case in the USA from 1878 to 1901 involving A.G. Bell, Thomas Alva Edison, Elisha Gray, Emil Berliner, Amos Dolbear, J. W. McDonagh, G. B. Richmond, W. L. Voelker, J. H. Irwin and Francis Blake Jr. Bell and the Bell Telephone Company eventually won that case, along with 600 other cases involving the invention of the telephone that went to trial. Another controversy involved Antonio Meucci. See https://w.wiki/78sh transmitted had to be formed by metal pins arranged on a rotating cylinder, so it was not very practical. In 1846, he patented a printing telegraph that printed Morse Code on moving paper tape using chemical rather than mechanical means. He also devised a punched paper tape system for prerecorded messages that could be transmitted quickly. It could send 325 words per minute, compared to the Morse system at only 40 words per minute. Samuel Morse claimed patent infringement, and the system was not widely used. Frederick Hale Holmes 1812-1875 continuous current electro generators Developed generators to power electric arc lighting in 1853. In 1856, he patented a magneto to power lighthouse arc lamps – see Fig.18. Heinrich Geißler 1814-1879 Geissler tube – early form of neon lighting Invented the Geissler tube in 1857, a partially evacuated glass tube filled with various gases with a high voltage applied between two electrodes, causing the emission of light by fluorescence – see Fig.19. The technology was a predecessor to neon lighting. Warren De la Rue incandescent light globe 1815-1889 He enclosed a platinum wire in an evacuated glass tube in 1840, creating an early incandescent light globe. Giovanni Caselli fax machine 1815-1891 Invented the first practical fax machine in 1861, called the “pantelegraph” (“pan” meaning all in Greek). You can see a photo of it at: https://w. wiki/78ro Ernst Werner von Siemens 1816-1892 pointer telegraph, speakers, electric lifts etc Invented the “pointer telegraph”, in which a message was received by needles pointing at letters rather than Morse Code. In 1847, he established Telegraphen-Bauanstalt von Siemens & Halske to produce it (see the video at https://youtu.be/v8DZuT5c2CI). Siemens AG is still an innovative company today. In 1874, he received US Patent 149,797 for a “Magneto-Electric Apparatus” for “obtaining the mechanical movement of an electrical coil from electrical currents transmitted through it”. Although not intended as a loudspeaker, that is what became of the invention. Alexander Bell was granted a patent for the telephone in 1876, which incorporated a moving-iron type loudspeaker. Subsequently, Siemens received German patent 2355 in 1877 for an improved speaker design with a moving coil transducer, a diaphragm as a sound radiator and a trumpet form as a cone. This was adapted by A. L. Thuras and E. C. Wente for use by the Bell System as a loudspeaker. In 1880, Siemens built the world’s first electric lift. He was the first to use gutta-percha latex to insulate telegraph cables, making the 1866 transatlantic telegraph cable possible. He also invented a practical dynamo and an electric railway. He also developed a process for galvanoplasty, plastics with gold or silver plating. The unit of conductivity, the siemens (S), is named after him. Scott de Martinville 1817-1879 phono-autograph Invented the earliest known device to record audio waveforms in 1857, the phonautograph (see Fig.20). However, these waveforms could not be played back. In 2008, some waveform images from 1860 were digitised and converted back into sound, thus becoming the earliest known intelligible Above: Ernst Werner von Siemens also invented the trolleybus, usually powered from overhead lines. Source: https://w.wiki/7Arv Fig.18: Frederick Hale Holmes’ generator from Souter Lighthouse. Source: https://w.wiki/7A2K (CC-BYSA-4.0). 20 Silicon Chip Fig.19: a Geissler tube in the form of a piece of modern art. Source: https://w. wiki/78sf (CC-BY-2.0). Australia's electronics magazine Fig.20 (right): a phonautograph visual recording, c.1859. Source: https://w.wiki/78sb siliconchip.com.au recording of a human voice. They were made 28 years before Thomas Edison’s wax cylinder phonograph recordings. James Prescott Joule 1818-1889 magnetostriction and Joule heating An English physicist in the field of thermodynamics who established the concept of energy conservation, showing that heat, electricity and mechanical work were interchangeable. He discovered the relationship between current, resistance, and heat generation, which led to Joule’s Law. The unit of energy, the joule (J), is named after him. He also did work in the area of magnetostriction. In 1843, he discovered the relationship between the heat dissipated by a resistor and the current through it. Resistance heating due to a current flow became known as Joule heating. Léon Foucault 1819-1868 eddy currents Credited with the discovery of eddy currents or “Foucault currents” in 1855, although these were first observed by Dominique François Jean Arago (see his entry on page 16). Charles S. Bradley 1819-1888 three-phase generator Built the first three-phase generator in the USA in 1887. Moses Gerrish Farmer 1820-1893 duplex telegraphy, electric locomotives, bulbs He investigated telluric currents, low-­ frequency currents that travel through the Earth or sea of natural or artificial origin. In 1847, he demonstrated an electric locomotive that pulled two passengers on tracks, powered by a nitric acid battery. Along with William F. Channing in 1849, he demonstrated an improved electric fire alarm system in 1857. In 1852, he made repeaters for a telegraph system and, in 1853, patented a method to transmit four messages on one telegraph line simultaneously. In 1859, he co-created the self-­exciting dynamo. He invented a current regulator for his electric lamps in 1859. The “Wallace-­Farmer 8 horsepower” (6kW) dynamo was used by Thomas Edison in early lighting demonstrations. He made an incandescent light globe, also in 1859, using a platinum filament and lit his house with them in July 1859, the first house to be lit by electric lighting (not Joseph Swan’s, as usually claimed). John Stephen Woolrich 1820-1850 Woolrich Electrical Generator He built the Woolrich Electrical Generator in 1844, the first generator used for an industrial process, commercial electroplating (see Fig.21). The voltage and current ratings are unknown. Edmond Becquerel 1820-1891 photo-voltaic cell He produced the first photovoltaic cell in 1839 (see Fig.22). When light was directed onto the device, voltage and current were produced. The photovoltaic effect is now known as the Becquerel effect. John Wellington Starr 1822-1846 carbon & platinum filament incandescent globes Filed patents in 1845 for two types of incandescent light globe, one based on a carbon filament and the other on a platinum filament. They were never commercialised. Nevertheless, the patent is considered the first important one on the road to a commercial electric light globe. There is quite an extensive story to John Starr and many uncertainties; see siliconchip. au/link/abn9 Hermann von Helmholtz 1821-1894 Fig.22: the first photovoltaic device from Edmond Becquerel. Source: www.pveducation.org/pvcdrom/ manufacturing-si-cells/firstphotovoltaic-devices arranged to provide a region with a close-to-uniform magnetic field. A Helmholtz resonator is an enclosed volume with a neck that resonates at a specific frequency. They are incorporated in some car exhaust systems to eliminate noise at certain frequencies, and this phenomenon is also the cause of ‘wind throb’ in a car with open windows at certain speeds. See the video titled “How to build a Helmholtz Resonator DIY” at https://youtu. be/JUsyeBkNVEI Lord Kelvin 1824-1907 bandwidth, mirror galvanometer etc Also known as William Thomson, developed and patented a system for submarine telegraph cable in 1855, with calculations of the achievable data rate in relation to cable diameter and copper purity (bandwidth). He was also awarded patents for a mirror galvanometer (1858) and “siphon recorder” (1867) to record messages. Helmholtz resonator and coil Fig.21: the Woolrich Electrical Generator, the first commercial generator. Source: https://w.wiki/78sc (CC-BY-SA-4.0). siliconchip.com.au Studied electrical resonance and invented the Helmholtz resonator during 1869-1871. He saw mechanics, heat, light, electricity and magnetism as a manifestation of a single force and published his ideas in “On the Conservation of Force” (in German) in 1877 – see siliconchip.au/link/abna Helmholtz also invented the Helmholtz coil, which is two electromagnets Australia's electronics magazine Lord Kelvin resting on a binnacle (housing for a ship’s compass) while holding a marine azimuth mirror. Source: https://w.wiki/7Arz October 2023  21 Thomson’s submarine telegraph system could send one character every 3.5 seconds. He also significantly contributed to thermodynamics; the absolute temperature unit Kelvin (K) is named after him. He invented the Kelvin balance that allowed the unit of current (the ampere) to be precisely defined. Gustav Robert Kirchhoff 1824-1887 Kirchhoff’s circuit laws He made significant contributions in the fields of electrical circuits, spectroscopy and the emission of blackbody radiation by heated objects. Kirchhoff’s circuit laws from 1845 are foundational to electrical engineering and physics. They allow an electrical network (circuit) to be analysed to determine the expected currents and voltages. Zénobe Gramme 1826-1901 Gramme machine (DC dynamo) In partnership with Hippolyte Fontaine, they built and manufactured an improved DC dynamo around 1873, called the Gramme machine, which produced smoother DC and higher voltages than prior machines. The duo also worked on other electrical devices. In 1873, he and Fontaine discovered that if the dynamo were connected to a DC supply, it would work as a much more powerful electric motor than any others at the time, which were of no practical use. Willoughby Smith 1828-1891 photo-conductivity Discovered photoconductivity in 1873 (when a material becomes more conductive upon exposure to light) in selenium. Sir Joseph Wilson Swan 1828-1914 first successful light globe Started experimenting with incandescent light globes in 1860, but was hampered by the lack of a good vacuum pump and a suitable power supply. In 1878-1879 he demonstrated the first incandescent light with a carbon filament in an evacuated globe, and he is regarded as the inventor of the first successful globe (see Fig.23). His house was claimed to be the first house to have electric lighting, but Moses Gerrish Farmer’s was likely first (see page 21). In 1881, he installed 1200 light globes in the Savoy Theatre in London, the first public building to have them. They were powered by an 88kW generator. Thomas Edison independently 22 Silicon Chip Fig.23: These carbon filament bulbs show the blackening effect. This is due to the evaporated carbon condensing on the inner surface of the bulb. Source: https://w.wiki/7As8 developed the light globe, and both men obtained patents in 1880. Swan sued Edison. This led to a joint company being formed in Great Britain in 1883, the Edison & Swan United Electric Light Company (“Ediswan”), to exploit the inventions. Edison and Swan produced successful light globes, but there were many ideas for globes before them, starting with Volta. David Edward Hughes 1830-1900 printing telegraph and microphone Developed a printing telegraph system in 1855. In 1878, he described electronic carbon-powder-based sound pickups called “transmitters”, then being developed for telephones. He demonstrated how they worked, superseding the prevailing theory of the time and coining the term “microphone”. He developed a type of microphone but never patented it, thinking the work should be available for the benefit of all. In 1879, he likely detected radio waves before Heinrich Rudolf Hertz did in 1887/1888, but attributed the phenomena to electromagnetic induction rather than radio waves. James Clerk Maxwell 1831-1879 Maxwell’s equations Discovered that electricity, magnetism and light were different manifestations of the same thing. He produced Maxwell’s equations in 186162, which are the basis of electrical circuit and light theory. They explain how electric and magnetic fields relate. Oliver Heaviside produced the modern form (the Maxwell-Heaviside equations). His work combining all previous observations, experiments and equations into a consistent electromagnetic theory set the foundation for much of Australia's electronics magazine Fig.24: a Crookes tube, the basis of the cathode ray tube (CRT). Source: D-Kuru/Wikimedia Commons – https://w.wiki/7BiD 20th-century physics and led to the era of modern physics. Henry Woodward & Matthew Evans incandescent light globe Together they obtained a Canadian patent in 1874, then US Patent 181,613 in 1876 for an incandescent light globe that used a carbon filament in a nitrogen-­filled enclosure. They did not have enough money to develop their invention, so they sold the patents to Thomas Edison in 1879. Sir William Crookes 1832-1919 Crookes tube – the basis of X-ray tubes Invented the Crookes tube (Fig.24) around 1869-1875. It is a partially evacuated glass tube with an anode at one end and a cold cathode at the other that produces cathode rays. The shape of the anode causes a shadow to be projected by the cathode rays (electrons), some of which are blocked by the shape, while others that pass to the outside. It is the basis of X-ray tubes and the cathode ray tube (CRT) as was commonly used for TVs, computer screens, radar displays and oscilloscopes. Some CRTs used heated cathodes. John Dixon Gibbs 1834-1912 power transformer With Lucien Gaulard, he demonstrated a power transformer in 1881 and obtained US patent 351,589 in 1886. While transformers were not a new idea, this was the first that could handle power at industrial levels. Johann Philipp Reis 1834-1874 Reis telephone and speaker Constructed a type of telephone in 1861 with a range of 100m (Fig.26). It incorporated a microphone based upon a parchment diaphragm that altered the electrical resistance between two contacts when it vibrated, siliconchip.com.au one of which was dipped in a drop of mercury. He also made a speaker that produced reasonable but weak sound, it was based on magnetostriction (ferromagnetic materials changing their shape when subjected to a magnetic field). Reis’ device could not reproduce speech intelligibly, so his patent was not upheld in a dispute with Alexander Graham Bell. However, David Edward Hughes later reported good results with the Reis telephone. Around 1947, the Reis device was tested by the British company STC, which confirmed it could transmit and receive speech, albeit faintly. The patent was partly invalidated because of a mistake in describing how the microphone worked; Reis said it worked by making and breaking electrical contact when it actually varied the resistance. Elisha Gray 1835-1901 Fig.25: the original writing and received copy on the Elisha Gray telautograph. Source: Popular Science Monthly, Volume 44, 1893-94. Musical Telegraph, telephone etc Invented an improved printing telegraph in 1872 (US patent 132,907). He also invented a “Musical Telegraph” that transmitted single musical tones over a telegraph link in 1874 (US patent 173,618). Oscillating steel reeds controlled by electromagnets produced the tones. See the video titled “Elisha Gray’s Musical Telegraph” at https://youtu.be/YxxsTdjT7PA Gray secretly built a prototype telephone in 1876. Alexander Graham Bell’s lawyer got to the patent office shortly before Gray’s lawyer; thus, Bell got credit for the invention. The true inventor of the telephone is still hotly contested. Gray is, however, known for inventing one of the first electric musical instruments (Fig.27). In 1887, he invented the telautograph, a precursor to the fax machine, although he is thought to have conceived the idea as early as 1874. He patented it in 1888 (US patent 386,814). A user’s handwriting was transmitted using a stylus attached to a mechanism that transmitted the stylus’ coordinates over a two-wire telegraph circuit (see Fig.25). The system became very popular. Fig.26: a Reis telephone consists of a transmitter, receiver (C) and a glass dome, all powered by a battery (B). siliconchip.com.au Australia's electronics magazine A telautograph can be seen in operation in the 1956 movie Earth VS The Flying Saucers on YouTube: https:// youtu.be/JCdnv3AP0eM?t=3683 William Grylls Adams 1836-1915 selenium produced an electric current Together with his student Richard Evan Day, they discovered that a platinum/selenium junction produced a current in 1876. Oberlin Smith 1840-1926 recording sound He proposed a method for recording sound by magnetic means in 1888. A thread such as cotton was coated with Fig.27: Elisha Gray’s Musical Telegraph from 1876. Source: https:// americanhistory.si.edu/collections/ search/object/nmah_703475 October 2023  23 or contained a magnetic powder or short lengths of fine wire, which were then magnetised by the current from a microphone source. His ideas were implemented by Valdemar Poulsen (see his entry next month) but it is unknown whether Poulsen was familiar with Smith’s work. Sir Hiram Maxim 1840-1916 electric lamps While famous for designing weapons, he also made significant contributions to the development of electric lighting, including improved methods of carbonising and manufacturing filaments for electric lamps. John William Strutt 1842-1919 Rayleigh scattering & waveguides Also known as Lord Rayleigh, made the first theoretical analysis of electromagnetic waves in a metal cylinder (waveguide) in 1897. He discovered what is now known as Rayleigh scattering, along with many other discoveries. Nikolay Benardos & Stanisław Olszewski arc welding They used a carbon arc to soften metals to a plastic state and, in 1881, demonstrated the first practical arc welding. Édouard Branly 1844-1940 coherer (radio signal detector) Invented the coherer, the first detector of radio signals in 1890, based upon the work of Onesti (see his entry next month). It consisted of iron filings in an insulating tube with two electrodes. Tivadar Puskás de Ditró 1844-1893 telephone and multiplex switchboard Invented the telephone switchboard in 1876. The first one was built by the Bell Telephone Company in 1877. In 1887, he invented the multiplex switchboard for more efficient resource sharing. Augustus Floyd Delafield 1845-1927 homopolar motor He received US patent 278,516 in 1883 for a “dynamo-electric machine” based on Faraday’s homopolar motor design. The video titled “The Homopolar Generator” at https://youtu.be/ cQ5Ueouk_VY shows how it works. Sir Mark Oliphant built a famous homopolar generator at Australian National University (ANU). It was one of the largest ever built and could deliver currents of 2MA. It operated from 1962 to 1986 and was designed to produce extremely high current pulses for applications such as rail guns. Wilhelm Conrad Röntgen 1845-1923 X-rays Was investigating vacuum tube equipment produced by others in 1895 when he discovered X-rays. He was performing experiments with a Crookes tube and fortuitously had some barium platinocyanide on his hand, a chemical known to fluoresce in UV light. He noticed it glowing out of the corner of his eye, an area of the eye that’s very sensitive to light. He had the barium platinocyanide because of experiments he was doing with a Lenard window tube, a Crookes tube with a thin window to allow some electrons to escape into the atmosphere. Alexander Lodygin 1847-1923 lamp. He sold the patent to General Electric in 1906. Pavel Yablochkov 1847-1894 carbon arc lamp Invented a kind of carbon arc lamp in 1876 called the “Yablochkov candle”. It would run for about two hours and could only be used once; it needed a large power source, produced a buzzing sound, UV rays, carbon monoxide and was a fire hazard. To power his lamps, Yablochkov invented a type of transformer based on Faraday’s discovery of induction to supply the required AC voltage for the lamps. The use of transformers to supply different voltages later became the basis of AC power distribution systems. Galileo Ferraris 1847-1897 polyphase alternator and induction motor He worked in the area of rotary magnetic fields in 1885. Such fields can be provided by a polyphase alternating current driving a system of coils or a single phase with windings arranged in a particular manner. His work led to the development of the polyphase alternator (effectively an AC motor operating in reverse) and the first induction (asynchronous) motor (Fig.28), but he did not patent it. He published his research on motors in 1888, just two months before Nikola Tesla obtained a patent for such motors. The invention of the polyphase alternator was a crucial event in the history of electrification. Alessandro Cruto 1847-1908 high-purity graphite light globe filaments Started experimenting with light globe filaments in 1880 and devised a carbon and metal filament lamps Fig.28: the world’s first AC motor from 1895 by Ferraris. Source: https://w. wiki/78se 24 Silicon Chip Later known as Alexandre de Lodyguine, obtained Russian and European patents in 1872 for a carbon filament lamp. In the 1890s, he invented some metal filament lamps and obtained US patent 575,002 for a tungsten filament Australia's electronics magazine Alexander Bell also co-founded AT&T. Source: https://w.wiki/7AsL siliconchip.com.au process of making high-purity graphite filament, which he demonstrated at the Electricity Expo in Munich in 1882. This filament was more efficient than that used in Edison’s globe and produced a white light, unlike Edison’s yellow light. Also, it lasted for 500 hours, while Edison’s original version only lasted 40 hours. He established a factory in Alpigano, Italy, producing 1000 globes per day. After disagreements, he resigned from the factory and, after many changes of hands, it was acquired by Philips in 1927. Alexander Graham Bell 1847-1922 telephone, photophone etc Bell is most famous for his work in developing telephony. In 1875, he developed an acoustic telegraph to send multiple telegraph messages on one line (ie, a multiplexing method). He filed US patent 174,465 in 1876 for the telephone, slightly before Elisha Gray (as noted earlier). Bell got his “instrument” (as he called it) to work for voice only three days after he got the patent, using a liquid transmitter (microphone) of Gray’s design; his first famous words on the device were to his assistant, Thomas Watson, “Mr Watson, come here, I want to see you”. Despite his achievements with the telephone, Bell regarded his greatest achievement as the photophone in 1880. This enabled voice transmission on a modulated light beam that travelled 213m in one experiment. It had no real application until the invention of the laser (1960) and the optical fibre (1965) for optical transmission of information. It was jointly Some of the oldest audio recordings A collection of early sound recordings and associated links are available at siliconchip.au/link/abni The following link is to a recording made by Alexander Graham Bell in 1885. It was recovered optically by 3D imaging the grooves of the wax disc recording: siliconchip.au/link/abnj You can also see a video where the author searched through old texts to find sound representations and digitally converted them to the original sounds at https://youtu.be/TESkh3hX5oM invented with his assistant Charles Sumner Tainter. Thomas Alva Edison 1847-1931 microphones, acoustic telegraphy, fuse etc Edison was a prolific inventor and entrepreneur. In 1873, he demonstrated the varying resistance of carbon grains in response to pressure and built a rheostat based on that idea, but abandoned it due to sensitivity to vibration. It was useless for its intended purpose in telegraphy but came in handy later for carbon powder microphones, which he tested in 1876. In 1875, he performed experiments in acoustic telegraphy, the name for multiplexing messages on telegraph lines, receiving US patent 182,996 in 1876. He filed for US patents 474,230, 474,231 & 474,232 for a “Speaking telegraph” in 1877, awarded in 1892. The patents took so long to be granted due to the competing claims of Alexander Graham Bell, Emile Berliner, Elisha Gray, Amos Dolbear, J.W. McDonagh, G.B. Richmond, W.L.W. Voeker, J.H. Irwin, Francis Blake Jr and others. In 1877, he invented a phonograph. The device recorded on tin foil and could only be used a few times; nevertheless, he gained fame for it. In 1878, he demonstrated the machine in Washington, DC and was celebrated as a genius. He received US patents 200,521 and 227,679 for it in 1878 and 1880, respectively. In 1878, he established the Edison Electric Light Company and said, “We will make electricity so cheap that only the rich will burn candles”. In 1879, he filed and, in 1880, received US patent 223,898 for an “Electric-lamp”. In 1880, he established the Edison Illuminating Company for electricity distribution in New York and, in 1882, opened the Pearl Street Station (600kW, 110V DC). In the 1880s and 1890s, there was the “War of the Currents”, the debate about whether electricity distribution systems should be DC or AC. Edison supported DC and saw AC as dangerous and unworkable. Edison invented a fuse in 1890 to protect his electrical distribution system. Next month That’s all we have room for in this issue. We will pick up where we left off in the second article next month, completing our chronological list of SC inventors. A replica of the upstairs level of Edison’s Menlo Park lab. Source: https://w. wiki/7AsR Also see our twopart series on Edison (September & October 2006; siliconchip.au/ Series/79). The Edison light bulb enclosed in a cage. 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T his potent monoblock amplifier uses a module designed by International Rectifier based on the IRS2092S Class-D controller and four IRFB4227 Mosfets – see Photo 1. This module is available from DigiKey ready-built for around $510. With some caveats, it can deliver up to 1700W RMS into 2W! That’s about the maximum audio output you could get from a single-phase mains 230V AC 10A supply. You don’t get super hifi performance at this dizzy level, but you will get very acceptable distortion (below 0.1% THD+N) at around 1000W. That’s very useful for large banks of PA speakers or music instrument reinforcement. Such monstrous power levels from domestic power supplies require a Class-D amplifier because of its high efficiency; in this case, it is 97% at 1700W. The module requires a very heavy-duty dual power supply at ±75V/18A, which will also be described in this article. The module is sold as an ‘evaluation board’ and has a few functions you can play with (eg, the ability to change the carrier frequency). It has very modest dimensions at just 192 × 149 × 56mm and only weighs 540g. It has a remarkably small heatsink, sufficient for ‘modest’ loads, but it can easily be enhanced, as we shall see. Not only does this amp put out enormous power, but it also has many essential protection features built in, like: • Output over-current protection (OCP), high side and low side, to handle clipping and accidental short circuits. • Supply over-voltage protection (OVP) over 82V. • Supply under-voltage protection (UVP) under 38V. • Output DC-offset protection (DCP) to prevent speaker damage in case of a fault. ◀ Photo 1: the pre-assembled IRAUDAMP9 mono Class-D amplifier module, wired up. Despite the relative complexity of the circuitry, using it is actually pretty easy. A thermal image of the amplifier module when delivering 400W (short term) is shown at left. The heatsink has only reached 44°C. At the same time, in the image at right, the 8W 800W dummy load dissipating 400W could boil water! 28 Silicon Chip Australia's electronics magazine siliconchip.com.au configuration). It does not apply to this mono amplifier. Amplifier Module Specifications » THD+N: typically <0.1% up to 1kW into 2Ω, 500W into 4Ω, 270W into 8Ω » Output power, 1% THD+N: 1.2kW into 2Ω, 575W into 4Ω, 315W into 8Ω » Load impedance: 2-8Ω » Dynamic range: 99.4dB » Residual noise, 20Hz-20kHz: 290μV » Damping factor: 81.9 (1kHz, 2Ω load) » Frequency response: ±1.25dB, 20Hz-20kHz (1W, 2Ω load) » Self-oscillating frequency: 300kHz (adjustable) » Gain: 33dB » Input sensitivity: 1V RMS input for 1kW into 2Ω » Modulation: second-order delta-sigma, self-oscillating » Power supply: ±48V to ±80V DC » Idle supply current: +67mA, -105mA » Idle power <at> ±72V: 13.2W » Efficiency: 74% <at> 100W, 94% <at> 1000W, 97% <at> 1700W » Heatsink temperature (unmodified): 56°C <at> idle, 104°C <at> 125W, 118°C <at> 1.2kW (shuts down after 130s) • Over-temperature protection (OTP) for a heatsink temperature over 100°C. The IRAUDAMP9 does not use a series relay to disconnect the speaker to prevent switch-on and switch-off thumps. Instead, it uses the IRS2092S’s on-chip noise reduction circuit which suppresses these transient events to levels below those generated by relays. Many copies of this module are available online, based on the same ICs. So while we recommend you purchase the known-good manufacturer version from a supplier like DigiKey, there are alternatives should it no longer be available. On the reference design, a lit red LED signifies a fault/shutdown condition. It also has a green LED that lights when conditions are normal. There are three switches on the reference design. S1 is a three-position switch that can select self-oscillation (middle position – “SELF”), internal (“INT”) or external (“EXT”) clock synchronisation. A BNC fitting is provided for the external clock, but no data is given for the amplitude, so we haven’t tried it. The purpose of S2 is not explained but it appears to control synchronisation between the clocks for two modules (eg, in a stereo or bridged Photo 2: the switchmode banks fit nicely into the aluminium toolbox; the kilowatt amplifier module occupies a small area on top mounted on plastic insulators. The small module on the right provides 12V from one of the 24V supplies to power the fan and VU Meter light (Photo 4). Note the large stainless bolts used to secure the switchmode power banks. siliconchip.com.au Australia's electronics magazine Operating principles and uses The IRAUDAMP9 reference design is a single-channel 1.7kW (into 2W) half-bridge Class-D audio power amplifier. At its heart is the IRS2092S Class-D audio controller that uses sigma-­delta PWM (pulse width modulation) to produce an audio signal with relatively low distortion and noise. An external gate buffer is also used to provide various protection modes, with the final power output coming from four IRFB4227 Mosfets. This module provides all the necessary housekeeping power supplies from the main ±75V for ease of use. The internally-generated power supplies include ±5V for analog signal processing (preamp etc) and a +12V supply (Vcc), referenced to –B, to supply the Class-D gate-driver stage. Above 1kW, it’s a good idea to use a larger heatsink than the one supplied (<2°C/W), especially for long-term use at high power levels. This is not a project for domestic use. Suitable applications include: • professional audio amplifiers and powered speakers; • active PA subwoofers; • other professional PA systems; • musical instrument amplifiers. Its manufacturer specifications are shown above, and we have produced three THD+N vs power level plots for standard load impedances in Fig.1. Those curves demonstrate it can easily deliver 1kW into a 2W load. Distortion Photo 3: six of these switchmode supplies give us an output of over 1kW into a 2W 2W load; three for the positive side and three for the negative side. They each have their own cooling fan and overload protection and are efficient and costeffective. Their output voltages are also adjustable. October 2023  29 Fig.1 (left): plots showing our measured THD+N vs power output for our complete prototype amplifier into three typical load impedances. 0.1% distortion at a massive 1000W is not bad! Fig.2 (right): this THD+N vs frequency plot into 8W reveals that distortion rises from around 300Hz. That is a little earlier than a good linear amplifier but is not unusual for a switching amplifier operating at a few hundred kilohertz. Typical program material has a lot of signal content below 1kHz, where the distortion level is pretty reasonable. rises quite a bit above 1kW, so if you want it to sound good, you can consider it a 1kW amplifier (that’s still a lot!). This module has a high PSRR (power supply rejection ratio), so you don’t need super smooth DC rails. It will reject 80dB of a 200mV peak ripple thanks to the balanced bipolar power supply. We used a ±80V 5A lab supply for some initial tests, then increased the power available to the module to 2,880W from six 24V DC 20A switchmode power supplies connected in series (see Photos 2 & 3), with additional capacitors for slightly improved performance. Those were two 10,000μF 100V chassis-­ mount electrolytic capacitors (Jaycar RU6712). converts the signal to lower resolution values with error diffusion/correction so that the final result, after filtering, reconstructs the desired signal accurately. In the case of a Class-D amplifier, the output only has two states (high or low), so it is effectively a 1-bit DAC, usually running at several hundred kilohertz. The delta-sigma modulator and filtering allow this to produce a signal in the audio range with an effective resolution of around 16 bits. Power output The quoted power output is 1700W RMS into 2W and we measured over 450W RMS into 8W. At these colossal power figures, you won’t get low distortion (in fact, the amp is already well into clipping), but at lower output levels like 1250W (2W) or 350W (8W), the distortion is not gross; see Fig.1. 2W loads are increasingly becoming the norm for modern big subwoofer drivers that demand this sort of power level. If using 4W or 8W drivers, you could parallel multiple to achieve 2W so that this amplifier can drive them at full power. Series/parallel sets with an overall impedance of 2W could be used to run many drivers from a single amp. Amplifier power output specifications Amplifier manufacturers (and their Delta-sigma modulation Delta-sigma (or sigma-delta) modulators (DSMs) are a class of oversampling digital-to-­ analog converters (DACs) that perform ‘quantisation noise shaping’ to achieve a high signal-to-noise ratio (SNR). They are an efficient solution for resolutions above approximately 12 bits. DSMs are extensively used in analog and RF applications. Effectively, a DSM involves using a low-resolution, highly oversampling DAC to reconstruct a signal with a much higher resolution but a lower frequency. The intended signal passes through a filter (usually digital) that 30 Silicon Chip Fig.3: the main distortion component is the third harmonic at -64.8dBv (0.05%), while the second harmonic is lower at -99.7dBv (0.001%). The delta-sigma design provides significant distortion cancellation. Australia's electronics magazine siliconchip.com.au Photo 4: this optional VU Meter gives you an idea of the current output level. designers) always want to find a way to publish the most impressive power specifications. Remember the ridiculous “PMPO – peak momentary power output” ratings where a small boombox was rated at over 1000W? Luckily, that isn’t the case here, as the >1kW ratings are real RMS power ratings, although you need a 2W load to achieve them. However, they are still a little cheeky in how they measure these power levels. You can get an inflated RMS power rating if you don’t care how much you distort the signal. Suppose you crank the gain or input signal level until the amplifier delivers an almost square wave into the load. In that case, you will get a rating about Photo 5: here, you can see the internal wiring of the speaker outputs with the 75μH inductor. The IEC mains input socket is under the black Jiffy box and is secured via screws and nuts on the base of the chassis to provide insulation and separation from the lower-voltage wiring above. 50% higher than you would with a more reasonable distortion level. The manufacturer states this is a 1.7kW amplifier, but that is at 10% distortion. We think it’s more realistic to rate it closer to 1kW (0.1% distortion). For PA use, you might be willing to accept a higher distortion level, so we’ve also given specifications at 1% THD+N (for example, 1.2kW into 2W). That’s approximately the point above which the output will start to sound lousy. Distortion As well as the plot of distortion vs power (Fig.1), we’ve also produced a plot of THD vs frequency for an 8W load, shown in Fig.2. As you’d expect Fig.4: the frequency response is pretty flat for 2W, 3W & 4W loads. For 8W loads, we recommend a 75μH series inductor to avoid that big spike at 25kHz, which could cause tweeter damage. siliconchip.com.au Australia's electronics magazine from a Class-D amplifier with a self-­ oscillation frequency of only around 300kHz, distortion rises significantly above 1kHz. Still, we already know this is not a hifi amplifier... Fig.3 shows the distortion spectrum for a 1kHz output at 1W. The first harmonic is -99.7dB <at> 2kHz (0.001% distortion), with the more critical third harmonic being -64.8dB <at> 3kHz (0.05% distortion). Frequency response The quoted frequency response by the supplier is ±1dB from 20Hz to 20kHz for a 2W load, but they didn’t give specifications for 4W or 8W loads. We made the plots shown in Fig.4, which reveal that with an 8W load, Photo 6: the rear panel has connections for the mains input (IEC), signal input (RCA) and binding posts for the speaker outputs. The top binding posts are for 2W & 4W loads, while the bottom posts provide frequency compensation for 8W loads. October 2023  31 there is a 7.25dB lift at 25kHz, at low power levels. The huge blip around 23kHz could easily destroy tweeters, especially at high power levels. Generally speaking, 2W, 3W or 4W loads are preferred for this board, and judging from the results, the IRAUDAMP9 was deliberately designed with lower load impedances in mind. We connected a 75μH 5A RF choke in series with the load and got the much more reasonable curve shown in orange. Therefore, our final amplifier design has a separate output for 8W loads fed via such a choke. Signal frequencies around 20kHz may cause LC resonance in the output low-pass filter, causing a large reactive current flow through the switching stage, especially if the amplifier is not connected to any load. This can activate over-current protection. Therefore, filtering out frequencies above 20kHz before feeding the signal to the amplifier is a good idea. That explains the 7.25dB spike we measured at around 20kHz with an 8W dummy load. Adding the extra choke fixed this, but it should only be used for 6-8W (nominal) loads. Listening tests After making all the measurements, we hooked up the amplifier to various speakers that presented 2W, 4W and 8W nominal loads. We were a bit nervous as such a huge power delivery would mean that, if anything went wrong, our speakers would immediately be toast! However, the switch-on was a letdown, as the module was silent except for the click of the switch and the quiet whirring of the cooling fans. The mute function from the IR2092S keeps the red LED on and the output muted for about three seconds. After that, the green LED switches on to indicate that the amplifier is functional. The amplifier mutes everything again at switch-off time after the DC supply voltage drops below ±38V. Switch-on and switch-off are absolutely silent; if it didn’t perform this way, speaker cones would probably pop out of their surrounds! Despite the compromised THD+N typical of Class-D amplifiers, the output sounds much better than expected, and the bass is undoubtedly effortless with all that available power. After playing several CDs, a quick check of the heatsink showed that it was merely warm and measured just 38°C with an infrared thermometer. Fig.5: this simplified circuit shows the overall configuration of the Class-D amplifier module, including the power Mosfets that drive the load and the bipolar transistor buffers that drive their gates. 32 Silicon Chip Australia's electronics magazine siliconchip.com.au The fan was able to cool everything, including the power supplies, which have their own internal fans. There are seven fans all up. With this sort of Class-D amplifier, efficiency improves as power increases, so there is likely no need for additional heatsinking. Class-D operation A simplified circuit diagram of the module, redrawn from the one provided in the data sheet, is shown in Fig.5. Capacitors C2int & C1int and resistor Rfreq form a second-order front-end integrator. This receives a rectangular feedback signal from the Class-D switching stage and produces a quadratic oscillatory waveform as a carrier signal. To create the modulated PWM signal, the input signal shifts the average value of this quadratic waveform (through the gain relationship between RFB, RFBfilt and Rin) so that the duty cycle varies according to the instantaneous value of the analog input signal. The IRS2092S input comparator processes the signal to create the required PWM signal, which is internally level shifted down to the negative supply rail where it is split into two signals, with opposite polarity and added dead time, to drive the high-side and low-side Mosfet gates, respectively. The IRS2092S drives two pairs of IRFB4227 TO-220 Mosfets in the power stage with PWM gate signals to drive the load. The amplified analog output is recreated by demodulating the PWM signal with an LC low-pass filter (LPF) formed by Lout and Cout, which filter out the switching carrier signal. Driving these pairs of Mosfets requires a peak of more than ±1A to drive the gates to rapidly charge and discharge their gate capacitance. To do this, a bipolar transistor emitter-­ follower buffer stage is used, comprising NPN & PNP transistors in totempole configuration, as shown in Fig.6. One pair is used for the low-side Mosfets and one for the high-side Mosfets. This buffering is necessary to achieve fast enough switching of the Mosfets to avoid exceeding the over-current protection voltage monitoring time. For over-current protection, the IC measures the voltage between the drain and source of the siliconchip.com.au Adjusting the Class-D switching frequency The total delay time inside the control loop determines the self-oscillating frequency. That includes delays from the logic circuits, the Mosfet gate driver, the external buffer, the IRFB4227 switching speed, the front-end integrator’s time constant, and variations in the supply voltages. Under normal conditions, the switching frequency is around 300kHz with no audio input signal and a ±75V supply. The PWM switching frequency greatly impacts the audio performance. Generally, distortion due to switching time becomes significant for higher frequencies, while at lower frequencies, the amplifier’s bandwidth suffers. Higher switching frequencies also result in higher switching loss in the power stage, so the thermal performance degrades. Another consideration when determining the switching frequency is to avoid it or one of the most significant harmonics causing interference in the AM broadcast band (531-1602kHz). If the switching frequency is 300kHz, its third harmonic at 900kHz could be a problem as it’s usually only 40dB below the switching frequency – see the diagram below. Adjustments are made by varying potentiometer P1 on the amplifier board with no input signal. The default amplifier switching frequency is 310kHz. The second harmonic is 60dB lower, but the third is just 40dB lower and could interfere with local AM radio stations. The carrier frequency is adjustable in case the interference causes problems with your local AM frequencies. Fig.6: this section shows just the output drivers and buffers. The bipolar transistors are needed as the IC can’t sink or source enough current to rapidly switch the relatively high-capacitance power Mosfet gates. Australia's electronics magazine October 2023  33 Parts List – 1kW Class-D Mono Amplifier 1 IRAUDAMP9 Class-D amplifier module [DigiKey IRAUDAMP9-ND] 6 24V 15-20A switchmode supplies [Mouser 709-LRS350-24, DigiKey 1866-3346-ND, element14 3596594, Wagner LRS-350-24, eBay 292508020804] 1 24V to 12V 1A+ DC/DC buck converter module [eBay 204144932095] 1 120mm 12V or 24V DC low-noise fan [Jaycar YX2584] 1 120mm fan guard [Jaycar YX2554 or YX2515] 1 100μH 5A toroidal inductor [Jaycar LF1270] 1 10kW 24mm logarithmic single-gang potentiometer plus knob [Jaycar RP3610 + HK7788] 2 red binding posts [Jaycar PT0460] 2 black binding posts [Jaycar PT0461] 1 chassis-mount IEC mains input socket with integral fuse and switch [Jaycar PP4003] 1 IEC mains input cable 1 10A M205 fast-blow fuse 1 panel-mount RCA socket to RCA socket [Jaycar PS0442] 1 1m RCA-RCA cable 1 high-efficiency fan heatsink (optional) [Jaycar HH8573] 1 small tube of thermal adhesive (optional, above heatsink) [Jaycar NM2014] 2 10,000μF 100V chassis-mount capacitors (optional) [Jaycar RU6712] 1 panel-mount VU meter (optional) [Altronics Q0490] 1 120kW ¼W 5% axial resistor (for optional VU Meter) 1 1N4148 small signal diode (for optional VU Meter) 1 UB5 Jiffy box Hardware 1 aluminium toolbox, 575 × 245 × 220mm or larger [eBay 192790170418, Bunnings 6120223] 4 M10 × 150mm cup head bolts and nuts [Bunnings 2310405] 4 M10 flat washers [Bunnings 2430052] 1 100 × 75mm aluminium pressed wall vent [Bunnings 0810902] 1 800mm length of 25 × 3mm aluminium flat bar [Bunnings 1079373 (3m length)] 1 800mm length of 20 × 10 × 2mm aluminium rectangular tube [Bunnings 1130559 (1m length)] 16 M4 × 20mm panhead machine screws and nuts [Bunnings 0168397] 18 M4 × 15mm panhead machine screws and nuts [Bunnings 0168393] 20 M4 × 10mm panhead machine screws and nuts [Bunnings 0247265] 36 M4 flat washers [Bunnings 0130531 × 3] 1 M4 shakeproof (toothed) washer 18 M3 × 20mm panhead machine screws and nuts [Bunnings 0247264] 20 M3 × 15mm panhead machine screws and nuts [Bunnings 0168388] 20 M3 × 10mm panhead machine screws and nuts [Bunnings 0247262] 6 M3 × 6mm panhead machine screws 4 M3 × 6mm countersunk head machine screws 4 M3 x 9mm tapped Nylon spacers (for mounting the amplifier module) 2 M3 hex nuts (for securing the Jiffy box) [Bunnings 2310899] 48 M3 flat washers [Bunnings 0257725 × 4] 2 M3.5 right-angle brackets [Jaycar HP0872] Wiring etc 7 6.4mm insulated female spade crimp lugs to suit 10A-rated mains wire 4 5.3mm eye crimp terminals to suit heavy duty hookup wire 4 5.3mm eye crimp terminals to suit heavy duty speaker wire 32 3.7mm forked spade crimp lugs to suit heavy duty wire 1 2m length of 10A mains-rated Earth (green/yellow striped) wire 1 2m length of 10A mains-rated light blue (Neutral) wire 1 2m length of 10A mains-rated brown (Active) wire 1 short length of heavy-duty figure-8 speaker cable 3 2m lengths of 15A heavy-duty hookup wire (red, black & blue) Cable ties (as required) [Jaycar HP1244] 34 Silicon Chip Australia's electronics magazine Mosfets, as they have a more-or-less fixed channel resistance, so that voltage is proportional to the load current. The IC starts monitoring this voltage as soon as the HO/LO outputs go high after a short leading-edge blanking time. The self-oscillating PWM modulator results in the lowest component count and highest performance. It represents an analog version of a second-­ order sigma-delta modulator, with the Class-D switching stage inside the feedback loop. Compared to carrier-signal-based modulation, the benefit of sigma-delta modulation is that all the error in the audible frequency range is shifted to the inaudible ultrasonic range. With sigma-delta modulation, we can apply sufficient error correction for low noise and distortion. The IRAUDAMP9 modulator incorporates: • a front-end integrator; • a pulse width modulator and level shifters; • gate driver and buffer; • power Mosfets; • output LPF. Input and output signals The input signal can be up to 2V RMS. Given that the IRAUDAMP9 module is a single-ended design (with the – output connected to ground) and it can drive 2W loads, that means that, in theory, you could use two such modules to drive a 4W load in bridge mode and achieve more than 2kW output! We haven’t tried this and can’t imagine it would be necessary outside of stadium-level sound reinforcement applications. Power supply The power requirements are very heavy, as you might expect for a 1kW+ amplifier. For initial testing, we used a lab power supply based on a 500VA 55-0-55V toroidal transformer that delivered ±80V DC but only up to 4A. This limited total power output to less than 450W into 2W. This power supply caused the amplifier to occasionally go into protection mode, mainly at frequencies below 25Hz, because of ‘bus pumping’, as described in the data sheet. This occurs since the IRAUDAMP9 is a half-bridge configuration. In regular operation, during the first half of the cycle, energy flows from one supply through the load and into the siliconchip.com.au other supply, causing a voltage imbalance. In the second half of the cycle, this condition is reversed, resulting in bus pumping of the other supply rail. The following conditions worsen bus pumping: • Lower frequencies (bus pumping duration is longer per half-cycle). • Higher power output voltage and/ or lower load impedance (more energy transfer between the supplies). • Smaller bus capacitors (the same energy will cause a larger voltage increase). Rather than use several expensive toroidal transformers and bridge rectifiers, as mentioned earlier, we purchased six 24V 20A switchmode supplies. We used three in series for the positive side and the other three for the negative side. The total cost for these was only $347, including delivery. This arrangement provides ±72V DC at 20A, although each independent supply is adjustable up to 25V, giving the recommended ±75V. Each side is adjustable to within 0.1V of the other, so PSRR is improved, and distortion and hum are significantly cancelled. This worked well, and all the graphs here were made with that supply configuration. You can also add extra capacitance to slightly reduce the distortion level, although that makes the amplifier a bit more expensive. Next month That just about covers how the amplifier works. Next month, we’ll have the details on how it goes SC together. Alternative Class-D module After our initial evaluation, we noticed that many alternative modules supposedly using similar components were available – see the photo below. We purchased one from eBay seller “polestarmascot” (www.ebay.com.au/ itm/325534592503) for a brief evaluation. This alternative board requires a separate low-voltage input of ±12V or 6-12V AC but has the added advantage of being a dual/stereo amplifier with a switch for putting them in bridged mono mode. It was very cost-effective at just $187, including delivery from China. We performed a brief evaluation of THD+N and frequency response. Its distortion performance was OK, giving around 0.02% at 1W/1kHz and 0.7% at 100W/1kHz into 8Ω. It actually had a pretty flat frequency response into 8Ω – much better than the IRAUDAMP9 with its big spike around 20kHz. Note that as there are many similar unbranded units for sale online, the components and construction are not standardised and may vary considerably. So our cursory tests really only apply to the unit we obtained. In brief, if you don’t want to spend around $575 on the genuine board, this one is around one-third the cost and does work but probably won’t give quite as good performance, especially at very high power levels. Specifications (from supplier) Supply voltage: ±33-80V plus ±12V or 6-12V AC Stereo power (±80V supply, distortion <0.1%): 2 × 350W into 8Ω, 2 × 700W into 4Ω, 2 × 900W into 2Ω (±62V supply, fan-assisted cooling) Mono (bridge mode) power: 1200W into 8Ω, 2000W into 4Ω (±70V supply) Gain: -33 times Input sensitivity: 1.6V RMS Input impedance: 20kΩ Frequency response: 0-50kHz ±1dB Residual noise: 200μV Dynamic range: >100dB Thermal cutout: 85°C Overvoltage protection: ±81V Efficiency: >90% at 300W We only performed some basic tests on this alternative Class-D amplifier module, but it seems reasonably capable compared to the (considerably more expensive) IRAUDAMP9, which uses the same major components. Fig.7: connections are straightforward; besides three wires for the ±75V DC power supply, you just need to connect an RCA cable for the input signal and two heavy-duty wires from the CH1 Output terminal block to the external output terminals for the load. siliconchip.com.au October 2023  35 Photographing Electronics By Kevin Poulter Creating quality images of electronic devices can be very beneficial for both hobby and business projects. For insurance, keeping track of disassembly and assembly during repairs, showing your achievements to friends, publishing in magazines like Silicon Chip and much more. Image source: https://unsplash.com/photos/HSXIp58yPyI odern cameras make it possible to M photograph like a pro, but just as importantly, you need to have good techniques. This article has some essential tips to help you get the best results. Your camera’s purchase price and number of pixels are less critical than how you use it. Silicon Chip regularly receives photographs that have the subject too far away, too light or dark, part of the item cut off and/or too many reflections. Most of those can be easily avoided with some awareness and practice. So here are some tips for excellent images. The camera Expensive cameras can make photography easier. Cameras costing about $300 upwards will usually give clear images. In that price range, they might start at around 14 megapixels (Mp or millions of pixels). Major newspapers photographed news and sports images in the early days of digital with just four-megapixel SLR (interchangeable lens) cameras. The number of pixels isn’t as important as the quality and size of the sensor. Larger, lower-noise sensors capture more light and so give much better results in less-than-ideal lighting conditions. A larger sensor will mean less noise in the image and less blur due to camera shake due to capturing images faster. However, they also require larger and more expensive lenses for the best results. If you’re going to buy a camera, the best advice we can give is to check multiple reviews (eg, on photography websites) and look at sample images to see if you are happy with them. For all-weather photography, you can set up a bench inside with diffused tungsten lamps, diffused LED lamps, or a monoblock flash, like the pros. Even the kitchen bench can be a temporary “studio”, as shown in Photos 1 & 2. Three factors are important when it comes to setting up a studio: 1. light brightness (in Lumens) 2. light colour balance & rendition 3. background Your “studio” Why have strong light? It usually results in a less noisy image (especially for cameras with small sensors, like those on smartphones). Significantly, it also improves the depth of focus, which photographers also describe as “depth of field”. Stronger light means you can use a higher aperture number (f-stop), resulting in a smaller imaging aperture, so the electronic device being photographed is in focus from front to rear. This is especially important in close-ups; otherwise, everything immediately in front of and behind the subject will be blurry. A higher aperture number means a The earliest photographers used daylight studios, and you can too. Direct sunlight gives strong shadows but can be diffused with something like a white sheet. Overcast skies give a much softer and more diffuse light, although the light is more blue than direct sunlight. Most modern cameras will compensate for that. A significant advantage of sunlight is that it’s so strong that you can stop your camera lens down for greater depth of field (more on that later). Also, as it’s what our eyes are used to, it results in excellent colour rendition (again, more on this below). Lumens Photos 1 & 2: these radios were photographed on a kitchen bench, with flat white panels behind. Light was bounced from the ceiling. The radios are branded Philips, Mullard and Fleetwood, all made by the Philips group of companies. The end result is shown in the right-most photo, with some post-processing done in Photoshop. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 3: bright LED lamps are available, like this Philips 27W version with 3000 lumens. It also has a high colour rendering index (CRI). smaller physical aperture for the light to pass through, which means less light will reach the sensor; hence, the need for brighter light and/or a more sensitive sensor. If your light is too intense for your camera’s maximum f-stop (meaning the images will be overexposed), you can move the light further away. As the distance from a light source increases, photons of light become spread over a wider area, resulting in the light intensity on the subject decreasing. Most cameras also let you decrease the sensor sensitivity (ISO or ASA) to overcome that problem. LED lamps are available in high lumens, like the Philips 27W bulb with 3000 lumens shown in Photo 3. Light colour Tungsten lamps project a very strong “warm” colour (yellow cast), so you are relying on camera settings like “auto white balance” to get the correct colours in your photos. It can be easier to use high-brightness ‘daylight’ LED lamps with a similar colour temperature to sunlight (around 6000K). Or go outdoors; see the “Photographing in sunlight” section below. Colour Rendering Index (CRI) The effect of a light source on colour appearance is expressed in the colour rendering index (CRI) on a scale of 0-100 (see Photo 4). Natural outdoor light at about noon has a CRI of 100 and is used as the standard of comparison for any other light source. CRI is not the same as a colour temperature in Kelvin because colour temperature only considers the average colour of light. CRI also depends on how evenly each wavelength of light is represented. A ‘daylight’ lamp at around 6000K could still have a very poor CRI if it’s only producing light at a few narrow wavelengths, making specific colours in objects you photograph look washed out or even the wrong colour entirely. This is one of the reasons it can be so hard to read resistor colour codes under artificial light! Philips states that the CRI of their LED lighting products is higher than 80. Look for lights with a CRI above 80 for good results with photography. Plain background An uncluttered background is important for a clear view of the product and to avoid nearby objects sharing their colour, reflection, or shape with the subject. A light (ideally white or grey) background will also help to bounce light onto the sides of the subject if you’re only illuminating it from one or two sources. One of the best backgrounds is very economical: a folding office wall planner/calendar on stiff card with a pure white background. It’s portable, usually super white on the rear, able to support reasonable weight and very inexpensive once it is out of date – see Photo 5. I paid $2 for an expired calendar in perfect condition. A folding one is best, or a bend can be scored. Photo 4: examples of the effect CRI can have on image colours. siliconchip.com.au Alternatively, 3mm or 5mm Corflute is available in white in several sizes at Bunnings or artist’s supply shops. Two pieces can be used, one vertical and another horizontal, butted to the vertical piece. Corflute is similar to cardboard but made from plastic (often used for political advertisements). A white project card can be curved for a seamless background for smaller electronic devices. Editor’s note: contrasting backgrounds are useful if you plan to remove the background using photo editing software. Cameras Many think, “I need a better camera to be a good photographer”. No! While there are undoubtedly inferior cameras, it is not so much the camera but how you use it that matters. A good photographer can get reasonable photos even with a fairly inexpensive camera (under some conditions, at least). Expensive cameras with high megapixels can make clearer images for poster prints, but that’s rarely needed. Some of the cover photographs for Radio Waves magazine were taken with cameras like the Nikon P900, which could be purchased for about $850 for a while. I have seen a $300 camera take very useful images; probably not cover material, but great for all other purposes. If you are looking for a good spec camera, the Nikon P950 or P1000 are very good fixed lens ‘superzoom’ cameras at about $1,300. The advantage is that the fixed zoom lens is very portable, and you don’t have to buy a lens separately; good SLR lenses can be expensive. Nikon, Canon and other brands also make more economical versions of zoom lens cameras. Photo 5: a calendar can be used as a backdrop. Australia's electronics magazine October 2023  37 My review of the similar earlier model, the P900, was published in the August 2015 issue (siliconchip. au/Article/8831). Decent SLR cameras with basic lenses are also available. The Nikon D7500 with a basic lens can be found between $1500 and $2000, but the Canon EOS 1500D is a bargain at around $700 for the body with an 18-55mm lens. It’s pretty basic for an SLR but still represents a big upgrade from a phone camera! “Mirrorless” cameras like the Sony ZV-E10 are popular these days and generally will be cheaper than an equivalent SLR. Still, we prefer the much clearer viewfinder on an SLR, despite SLR cameras being a bit bulkier and more expensive. Mobile phones Mobile phone cameras now have around 100 megapixels, so they must be good, right? Mostly they are not ready for high-quality magazine shoots, as it’s not the megapixels but how they capture and process the images. Despite this, mobile phone owners, the author included, take many snapshots on mobile phones due to the convenience (“the best camera is the one you have with you!”). The cover for the January 2022 issue of Radio Waves was shot on an iPhone by David Bartlett under incandescent light, so I removed the yellow cast, made the background white and sharpened the image, all in Photoshop. The result was pretty good – see Photo 6. Alternative to Photoshop The camera is important, but post-processing is, too. Processing can convert a photo that’s just OK into a great one as long as its fundamentals are fine (the subject is in the frame, in focus, not overexposed etc). A free software program called GIMP is available for Windows, macOS and Linux. It can do much of the image manipulation that’s possible in Photoshop (although not all). However, be careful you download from the official site, which is www. gimp.org/downloads/ We sometimes use it on computers that don’t have Photoshop for basic image manipulation as it is not worth Photo 6: this cover image was taken with an iPhone. It needed a fair bit of processing but turned out OK. Photo 7 (above): purchase camera memory cards from reputable suppliers and brands. 38 Silicon Chip Australia's electronics magazine paying $30+ per month just to do basic jobs like removing backgrounds or adjusting colour balance. There are some extra steps if you plan to edit RAW images in GIMP, as it cannot natively open that file type. There is also a free add-on called darktable that adds that capability (www. darktable.org). Good foundations What makes a good photograph of an electronic device? It should be a clear image that shows the whole object with all its details, in the right colour, at the right angle and with a plain background. Camera instruction manuals can be daunting. However, reading the book and making a few “once only” adjustments to the camera will reap the reward of consistently good images. Important camera settings include: 1. Choose the highest resolution available with the least compression. That will fill your memory card quicker; however, a 32GB card will still hold about 3000 images. 2. Save to JPG/JPEG, as it is the main file option on most cameras. JPEG is a lossy system, but if you choose the least compression/largest file, it compares extremely well to lossless formats like TIFF. 3. Some cameras have a “save to RAW” option. RAW enables a broader range of adjustments to be made after the photograph is saved but uses significantly more space on the memory card, takes longer to read/write and takes more time to complete a finished image. Like many professionals, I don’t use RAW at all. 4. Automatic exposure and autofocus are recommended. Both should be set to centre spot if that’s in the menu list. Aim the autofocus centre spot toward the most critical area to be in focus; for example, the tuning dial of a radio. Manual focus and exposure can be experimented with later on. I only use manual focus about once a year. 5. The camera is likely already set to auto white balance at the factory, although that is worth checking. In summary, check that the following are set, if not already: highest resolution, JPG, centre spot auto exposure, centre spot autofocus and auto white balance. Importantly, take one or two photos with your preferred settings at the start of a photo session and then look siliconchip.com.au Photo 8 (left): a radio photographed under less than optimum lighting. at them. Ensure you’re happy with the exposure, depth of field, colour balance etc. Tweak settings like exposure compensation and f-stop if necessary. It’s much easier to make one or two changes at the start than to take dozens of photos only to find they all have the same problem! Photo 9 (below): the same radio photographed in midday sunlight. Note the mirrors and black card controlling reflections. You can see how the blue card in the background is reflected by the radio, showing why using neutral colours is important. The card in the foreground keeps the front panel dark and neutral; however, some reflection was left in the upper front panel to show the pattern in the Bakelite. Memory cards Get your memory cards from a wellknown brand with a decent capacity from a trustworthy supplier. Some dodgy online sellers label a small-­ capacity card with a much higher number. You could lose many images if the capacity is fake or the card is low quality and fails. A friend used a card for a once-only event and found the photos were nearly totally lost. The camera manual will state the maximum capacity and card type that suits. A 32GB card (like in Photo 7) may hold up to 3000 high-res images in some cameras. Be sure to download images to external storage like a computer regularly, or you could lose all your pictures if there is a glitch. Lighting Lighting is probably the single most important aspect of getting good photos. You usually want fairly even illumination without harsh shadows, and it needs to be bright enough to avoid sensor noise and to give you the desired depth of field. It also needs to provide a good CRI, as described earlier. On-camera flashes are convenient but generally unsuitable for shooting electronics because too much light is reflected directly back to the camera, causing flare. If you get a high-end flash for an SLR, you can use bounce flash, where the light bounces off the ceiling, but that’s still far from ideal. Professional photographers have a studio with expensive lighting to produce top-quality photographs at any time, regardless of the weather. You can set up a home bench or workbench studio, and some readers have. It can be temporary if you don’t mind carting the lights and other gear out when you need to take some photos, then putting them away afterwards. Photo 10 of the AWA “Big Brother” shows what can be achieved outdoors in sunlight or cloudy bright conditions. It is important to control the light, indoors or outside, or the image siliconchip.com.au may look flat with no detail, like in Photo 8. Preparing the item Quality images reveal blemishes, including dust, so clean and detail the device. It is amazing how much dust shows in a photograph that was not evident when setting up. Some can be retouched later in an application like Photoshop or GIMP, but it’s best to save computer time and effort by cleaning the device first. You also risk losing detail if you do too much post-processing. If you have an air compressor with an oil separator, you can blow off much of the dust with an appropriate nozzle. You can also remove dust with a cloth, but it’s pretty tricky to clean a PCB that way, as you generally can’t get between the components very well. You can Australia's electronics magazine Photo 10: the resulting photo from the setup in Photo 9. Similar results can be obtained indoors with LED lights or studio flash units. October 2023  39 Photo 11: photographing this radio on patterned glass gives an interesting effect. dampen the cloth for external surfaces to improve dust adhesion or use a special dusting cloth. Consider whether you want any power cords or other cables in the shot. Generally, it’s better to hide them behind the device or have them go out of the frame. If a front panel knob or similar is missing, you could fix that in post-processing with a bit of copying and pasting, but you need to know what you are doing if you don’t want it to look obviously fake! Knobs can look neat if they are all on the same angle, similar to how commercial photographers set a watch to ten past ten for the best images. If the device you’re photographing has a screen (especially a touchscreen), give it a bit of a wipe before photography to remove any fingerprints and such. Do the same for any glass or glossy parts of a device, as they tend to pick up marks easily. Lights on or off? If the device is not fully operational, it is not essential to have the 40 Silicon Chip lights illuminated. The example AWA radio was not powered up for the photos. Instead, the dial was brightened in Photoshop, and a yellow tint was added to resemble the appearance of low-power incandescent dial lamps. If you are taking photos in bright light (as we recommend), it will often overpower any lights or screen images, making them look like they are off, even if they are on. If you need to capture the lights/ screen illumination, you will have to take a second photo from the same angle in darkness with a steady camera (eg, on a tripod) to avoid blur. The light/screen images can then be composited onto the main image taken in bright light to reproduce what the human eye sees. Photographing in sunlight For photographing this AWA Big Brother, the budget was about $25 $30, and these items can be reused again and again: ● A calendar/planner poster or Corflute pieces. Australia's electronics magazine ● Three black project poster cards. About $10 total, and can be purchased from stationery stores. ● Two or three mirrors, A4 size or slightly smaller (see Photo 9). Available from discount variety stores. The most common cheap mirrors are usually acrylic, so they won’t cut or shatter by accident. ● Blu-Tack and stable containers, like bottles or cans, to tilt the mirrors at extreme angles if needed. Bright midday light is best – sunny or bright cloudy – as it ensures the best depth of focus and, most likely, the best colour temperature. Choose the highest aperture f-stop available on your camera (for SLRs, it’s often f/22) for the best depth of field unless you are planning on purposefully blurring the background. In that case, you’ll have to experiment with the f-stop to get just enough depth of field for the subject. If the weather is strongly overcast, the images may exhibit a strong blue cast unless your camera has very good auto white balance. The images will be quite soft, too; that might be what you want, depending on your goals. Avoid early morning and late afternoon daylight photography, as the resulting images will have a yellow tint. The sun or artificial light is best ‘over your shoulder’. If your camera can’t fully correct for the yellow/blue cast, you can still do it later in post-processing. It’s a good idea to have a white object (like a sheet of printer paper or a small white card) somewhere in the frame to make that easier. However, that object must not be overexposed to be used as a white reference. Note that mirrors can also be used in studios, reducing the need for so many expensive flash units. The method for taking the photograph shown in Photo 10 was: 1. Place the device (in this case, a radio) on a table, with the white background in position. 2. Select an angle that shows some of the side and part of the top of the device. 3. Chances are you will see reflections and bright areas. You may even see colour casts from nearby objects, like walls. Nearly always, the top of the device and one side is way too bright. So strategically place pieces of black card to fix these. 4. Some devices like the AWA Big siliconchip.com.au Brother radio look best with their curves and features highlighted. This is a visual adjustment by trial and error, using mirrors or white cards. To avoid too much overall highlighting, the AWA had less mirror highlighting on the left side of the picture. This was achieved by changing the angle of the mirror. Moving the mirror further away also reduces highlights. 5. During photography, change the shooting angle to give plenty of choices for the later selection of images. Digital photography is essentially free, so take many extra photos until you are experienced. Many cameras enable auto-focus when the shutter is pressed halfway down; aim at something that needs to be crisp or an object in the middle of the device. In this case, I used the radio dial. 6. It’s generally best to avoid wide-­ angle lenses or zoom lens settings less than 50mm, as they will distort the image. Even high-end wide-angle lenses can’t prevent the visual oddity inherent in wide-angle photography. Long telephoto lenses can make an image seem flat, so the best choice is usually between 50mm and 200mm (35mm equivalent). 7. Crop the subject to near full frame to achieve the best resolution. If the image has a generous border around it, the resolution/clarity of the subject may be lowered (this is less of a concern with high-megapixel cameras). However, it’s better to err on the side of having too much border than cutting any part of the subject off, as the former will still give you a usable image! 8. Carefully look at the results in your camera preview indoors, where the most detail can be seen. It is good to be picky because taking more photographs at this stage is so easy. Zoom in to check the details. 9. Now you’re ready to make post-photography adjustments. If the device was photographed on a white background, the image may be ready to use out of the camera. Note how the top of the radio (in Photo 9) is a good tone as it is reflecting the black card above. The same applies to the side. The black card in front of the radio reduces a very light area that appeared when it was placed on the white background. The horizontal highlights are from the sun, while the vertical highlights were created by the mirrors directing the sun. If cards and mirrors can be seen in the final photo, the radio background can be cut out in a graphics application. In this example, some small areas had a colour cast, so in Photoshop, an eyedropper was placed in a good area of the case’s colour, a lasso drawn over the colour cast and a new layer opened. The lasso area was filled with the best colour, and the layer’s setting changed to ‘colour’ to remove the tint. Many specks of dust were also removed using the ‘stamp’ and ‘dust and scratches’ tools. Then, the dial was adjusted for more contrast, brightened, sharpened, and a yellow tint was added to make it look like it was illuminated. You don’t need to do that much post-processing; the cleaner you can make the image from the camera by tweaking the setup, the less fiddling will be required later to get the best result. Reflections for great style There are several ways to photograph electronic devices like radios on a reflective surface to achieve a classy result – see Photos 11-13. Consider Laminex, a kitchen bench, or a piece of glass or acrylic on top of a colour. The lower the angle of view, the stronger the reflection shows. From screen to paper One of the biggest challenges when working on an image on a computer screen is that it can look perfect, with plenty of detail, because the image is backlit. Ultimately knowing how to set the final colour, brightness and contrast so it looks good in print comes from experience. If the end goal is Photo 12 & 13: an Astor GS photographed on Laminex. The unedited photo is shown at left, while the right-hand photo has a background, and other post-processing, added in Photoshop. siliconchip.com.au Australia's electronics magazine October 2023  41 Photos 14 & 15: Both of these photos were taken without a macro lens. The left image was taken with a mobile phone; the resistors are just 6mm long. The right image was taken by an iPad, and is of an area just 55mm in width; with two suspect joints circled in red. It was lit by a desk magnifier with a LED and the resultant photo slightly sharpened. colour prints, you can have some small test prints made first. The colour can be glaringly wrong in print, even though it looked correct on the computer. Remember that a computer screen usually uses RGB colour while printing is almost always CMYK. CMYK processes can’t reproduce all RGB colours (and vice versa). Converting the image to CMYK, then viewing it on-screen can give you some idea of how it might look in print. Fortunately, the colour should be good if the image was taken around noon on a sunny day. You could also invest in a monitor calibration device (or a monitor with good out-of-thebox colour performance) so you know that what you’re seeing is reasonably accurate. When an image is dark and not showing a range of tones, either photograph it again with mirrors lighting dark areas, or use the “Shadows & Highlights” adjustment in Photoshop (or the Colours → Shadows-Highlights menu option in GIMP). Adjusting the Original image’s ‘curves’ via the Curves menu option can also help to improve tonal problems, including where it looks washed out or too stark. With the device opened up, it may be very hard to see internal components like the speaker deep in the ‘cave’. Flash-on-camera (or more mirrors) can help with this. Try a few different angles to reduce flash highlight shine. the yellow setting to much lower. I then slightly reduced the wide-angle lens perspective using the Perspective tool, followed by lightening and sharpening the dial. Finally, I removed the background by tracing around the radio and deleting the unwanted part of the image. Editor’s note: Photoshop also has built-in lens correction under the Filter menu where you can select from a variety of different camera makes, models and lenses. Photographing with a phone Close-up shots As mentioned earlier, if you have a Original modern phone with a high-spec camera, that could work for medium-­size prints or on-screen display. Looking at the turquoise radio on the cover of the January 2022 Radio Waves, the iPhone made an acceptable photograph. Dave Bartlett photographed the radio on a table under an incandescent light. Upon receiving his image, I corrected the strong warm yellow colour cast using the Photoshop colour adjustment menu, especially moving An expensive macro lens is likely not needed for close-ups. Using a camera, move in as close as possible, then enlarge the resulting image – see Photos 14 & 15 as examples. Or try a mobile phone or iPad if they have a close-up facility. The smaller sensors in mobile devices make taking close-up photos easier. You also have the option of cropping an image and ‘blowing it up’ on the computer if you can’t get close enough with your lens. The earlier comment about removing dust is only magnified by macro photography. Photo 14 shows how important it is! Editor’s note: many SLR lenses have a fairly large minimum focus distance. To overcome this, we purchased the “AF-S VR Micro Nikkor 105mm f/2.8G IF ED” for our Nikon SLR camera. While expensive, it is the best macro lens we’ve tried, bar none – see Photo 16. We recommend it if you can afford it! Its vibration reduction (VR) function makes handheld shooting easy, too. SC Photographing inside a device Enhanced (below) Photo 16: the cropped output of Silicon Chip’s camera with the Nikkor 105mm macro lens (left), plus an enhancement of a section of that image (right). As the original was shot with a ‘softbox’ light, it’s a little soft, so it was sharpened, along with other enhancements, to compensate. Enhanced (below) 42 Silicon Chip Australia's electronics magazine siliconchip.com.au Ventilation Fans We stock a wide range of DC and AC powered enclosure fans to keep your projects cool. A GREAT RANGE AT GREAT PRICES. 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Jaycar reserves the right to change prices if and when required. Project by Andrew Woodfield, ZL2PD 2m VHF FM Test Signal Generator This Test Oscillator uses an AD9834 DDS chip in a somewhat unusual way, producing signals in the 2m band (144-148MHz) even though that is well above its 80MHz oscillator frequency. It can produce a CW signal at three different levels and optionally add frequency modulation. T he Analog Devices AD9834 direct digital synthesis (DDS) chip is a common feature of audio function generators and HF oscillators. This unusual variation delivers programmable FM digitally generated signals on channels across the 2m amateur radio band. It can even run from a single AA-size cell. The 2m amateur radio band covers 144-148MHz in Australia, New Zealand and North America, or 144146MHz across Europe. Designs using the inexpensive AD9834 have been published for over 20 years. Yet, looking closely, almost all designs mimic the circuits from AD application notes, with the differences primarily being the choice of microcontroller, display and PCB layout. Several years ago, I made a simple test board with an ATtiny45 microcontroller and a couple of pushbuttons. I tested the AD9834’s overclocking potential and several DDS output filter designs and quickly established that the AD9834-BRUZ chips could be overclocked at up to 85MHz, a useful margin over the 50MHz specification from the data sheet. The slightly more expensive -CRUZ devices are rated at 75MHz but are reported to handle 100MHz clocks. That was the limit of my interest in the AD9834. I had no immediate use for it and put it on my shelf. Features & Specifications ▬ 144 to 148MHz output in 500kHz steps ▬ Four additional user-programmable memory frequencies in the 2m band ▬ -45dBm, -75dBm and -105dBm output levels ▬ Carrier-only (no modulation) or FM ▬ ±3kHz FM deviation (1kHz tone) ▬ CTCSS and external modulation audio inputs ▬ Simple to align output filter; everything else is digital 44 Silicon Chip Australia's electronics magazine So I expected few surprises when a friend recently asked me to confirm the results he was measuring on his AD9834 signal generator design. Phase modulation As I worked on these tests, the claimed frequency modulation (FM) and phase modulation (PM) features headlined in the data sheet caught my eye. In my previous DDS designs with the AD9850 and AD9851 chips, their limited phase registers made them unsuitable for FM. The AD9834 variable-frequency oscillator (VFO) designs I’d seen only used the DDS chip as a variable RF oscillator or audio function generator. I’d never seen any mention of AD9834 phase modulation anywhere before. Looking more closely, I realised that the AD9834 has far more capable 12-bit phase registers than the AD9850/9851. That made me curious. Within an hour, I had phase modulation ‘working’ in a limited fashion. However, it wasn’t clear from the data sheet how to get a specific modulation level. An extensive search of Analog Devices application information showed they were also largely silent on the topic. As I continued to explore phase modulation, the calculations, and the other features of the chip, I realised it could achieve something quite different to the usual AD9834 design. This novel 2m CW/FM test oscillator is the result. DDS and alias frequencies The AD9834 is a DDS oscillator chip typical of many made by Analog Devices. The block diagram (Fig.1) shows the internal arrangement. It contains a pair of programmable Frequency Registers and a pair of Phase Registers to allow the selection of one of two combinations of frequency and phase. These registers control a powerful numerically controlled oscillator (NCO) using the chip’s 28-bit Phase Accumulator. The output of the NCO drives a lookup table and 10-bit DAC that converts the NCO output to a sinewave. The output frequency, fout, can be calculated as fout = Nreg × fclk ÷ 228, where fclk is the external clock frequency, and Nreg is the 28-bit digital value loaded into one of the two selectable frequency registers. The siliconchip.com.au associated Phase Registers allow the output signal phase to be shifted by a programmable phase angle. With an external crystal clock and a suitable low pass filter (LPF), the AD9834’s output is a reasonably clean, low-noise sinewave that can reach up to about 30MHz. It’s possible to generate frequencies with a resolution of 0.3Hz. The output frequency’s accuracy depends on the crystal oscillator’s precision and stability. Actually, the output produced by the DDS is significantly more complex than this. In the absence of the output LPF, the DDS process also generates an extended series of signals along with the main output signal. These can reach well beyond 300MHz, as shown in Fig.2 (also from the data sheet, again with a bit of colour added). The primary output signal (fout) is typically filtered by an LPF that heavily attenuates these other unwanted signals. The output may be programmed to any frequency up to half the external DDS clock frequency, eg, 40MHz if the DDS uses a clock frequency of 80MHz. Those unwanted products generated by the AD9834 are called ‘alias’ or ‘image’ signals. The first is on a frequency of fclk − fout. When the DDS clock is 80MHz, if fout is changed in steps from 1Hz to, say, 30MHz by changing the value programmed into the AD9834’s Frequency Register, this first ‘alias’ signal (labelled fc − fout in Fig.2) is generated. It begins at 80MHz and reduces in frequency with each step, down to 50MHz (50MHz = 80MHz – 30MHz). These are shown in more detail in Fig.3. If the ‘wanted’ fout signal moves towards 40MHz (half the DDS clock frequency), this first alias output product becomes increasingly annoying. It also approaches 40MHz from above and must somehow be filtered out. That becomes more and more difficult as the desired fout signal rises above 30MHz and approaches 40MHz. This demands the use of a low pass filter with a very steep cutoff for most applications. Such filters usually start attenuating just above 30MHz, with the rejection increasing sharply to reach at least 60dB by 40MHz. Most designs use a complex 5th- or 7th-­ order output low-pass filter for this reason. siliconchip.com.au Fig.1: the AD9834 block diagram, reproduced from the data sheet (with some added colour). It is a typical DDS oscillator with a 28-bit phase accumulator that can generate accurate RF sinewaves up to 30MHz from an 80MHz external clock. Fig.2: without any added filters, the AD9834’s output signals extend well beyond 300MHz. Fig.3: the AD9834 output spectrum with an 80MHz DDS clock and the frequency register set to 14MHz. The arrows show the direction the unfiltered alias carriers travel as the frequency of the 14MHz fundamental increases. The green dashed line shows the typical high-order low-pass filter normally used to remove these other products from the output signal. Australia's electronics magazine October 2023  45 You can also see from Fig.3 that the DDS output level is not the same across the spectrum. The output level falls following a sin(x) ÷ x response. With an 80MHz clock, for example, the output at 30MHz is 2dB less than at 1MHz. The 50MHz ‘alias’ output generated when the main output is 30MHz is 6.5dB below the 1MHz level, and only 4.5dB below the 30MHz wanted output. So, without a good LPF, the AD9834 output at 30MHz would have severe distortion due to the desired signal mixing with the nearby unwanted 50MHz alias output product. 145MHz, 146MHz, 147MHz and 148MHz respectively, albeit at much lower levels. If a relatively narrow bandwidth LC bandpass filter is added to the AD9834 output and tuned to the 2m band, passing just these 2m-band signals is possible. An example of the response of such a filter for use with the AD9834 is shown in Fig.4. This output filter must also be designed to match the 200W output impedance of the AD9834 and allow for a 50W output load impedance, to match the expected loads in typical RF applications. Operating the AD9834 in the 2m band (144-148MHz) Modulation Fig.3 shows the other alias signals generated above the desired and first alias outputs. If the desired output is 14MHz and the first alias is 66MHz, the next alias output is 94MHz. More alias outputs are generated at 146MHz, 174MHz, 226MHz and beyond. The AD9834 output also contains a residual clock output at 80MHz. Since it is a square wave clock, it has a strong unwanted product at the third clock harmonic, 240MHz in this case. Fig.3 also shows the direction the aliases move as the main carrier increases in frequency. Alias outputs can appear in the 2m band, for example, if the AD9834 output is set in turn to 16MHz, 15MHz, 14MHz, 13MHz and 12MHz with an 80MHz DDS clock, the third-image alias output (‘super-Nyquist’ product) will be generated at 144MHz, With this filter selecting the 2m band signals from the AD9834 output, the next step was to see if it was possible to achieve frequency modulation with the chip. As noted earlier, the AD9834 data sheet highlights the possibility of phase (and thus frequency) modulation but gives no further detail. Analog Devices’ application notes did not provide any further details about how the AD9834 phase modulation registers might be used to achieve this. Also, despite a thorough search, I could not find any DDS design in which this feature was actually used. That led me to dig further into phase modulation. I analysed and tested the AD9834 Phase Registers to understand their impact on the DDS output signal. When FM was emerging on the 2m VHF amateur radio band from 1970 to 1980, phase modulation (PM) was generally considered the preferred Fig.4: a bandpass filter using discrete inductors and capacitors can give this response, which allows the 144148MHz alias output product to be selected while other alias, clock and fundamental signals are rejected. 46 Silicon Chip approach. There were claims of “better quality” modulation and “more natural sounding” voices. However, there was little to suggest any evidence supporting these claims. Practical issues, and the arrival of cheap varicap diodes, led to PM being quickly overwhelmed by FM. Varicaps were easy to use in oscillators and often reduced the component count, unfortunately sometimes at the expense of modulation linearity. PM quickly fell out of favour, and that may have led to the minimal information about phase modulation in the technical magazines, handbooks and reference textbooks of the period. One useful source from those days was William Orr’s classic “Radio Handbook”. The 1981 edition briefly described the method and provided a few examples; see my summary in Fig.5. First, the transmitter’s frequency deviation (ie, modulation) is directly proportional to the amplitude of the input audio signal level for both phase modulation and frequency modulation. With FM, the frequency deviation remains constant regardless of the input signal’s frequency. However, with PM, the deviation increases with increasing frequency. Since phase-modulated transmitters were initially more popular, the characteristic PM frequency response, later referred to as ‘pre-emphasis’, also required the reverse audio frequency characteristic to be implemented in the receiver, ie, ‘de-emphasis’. This Fig.5: the frequency deviation of a phase- or frequencymodulated transmitter depends on the modulation level, but phase-modulated transmitter deviation also depends on the input modulation frequency. (Adapted from Bill Orr’s “Radio Handbook”, 1981) Australia's electronics magazine siliconchip.com.au is usually achieved by a simple RC circuit located immediately after the FM receiver’s discriminator (detector) stage. FM transmitters required the addition of this pre-emphasis characteristic to work correctly with those FM receivers. A similar RC circuit was usually added just ahead of the FM modulator to mimic phase modulation. Since the effect of noise increases with audio frequency, adding pre-­ emphasis to FM (or just using phase modulation with its integral pre-­ emphasis characteristic) improves noise performance. AD9834 phase modulation With that background, let’s return to the AD9834. Phase modulation in the AD9834 is produced by making periodic changes to the value stored in the Phase Register (PHASE0/1 REG; see Fig.1). The Phase Register’s value results in a precise phase shift of the current DDS output signal. The DDS output frequency is determined by the value in the AD9834’s Frequency Register. The AD9834’s Phase Register value shifts the phase of the fout carrier by 2π ÷ 4096 multiplied by the value contained in the Phase Register. The Analog Devices data sheet doesn’t explicitly state this, but that’s what it does. As to the lack of any application of this information, any example, or further supporting detail, AD9834 users are left to fathom the usefulness of this relationship for themselves. As it turns out, by periodically storing a value proportional to the amplitude of an incoming audio signal in the AD9834’s 12-bit Phase Register, it is possible to produce the desired PM (and thus FM) signal. There should, by rights, be a fanfare of trumpets at this point in the story, but there’s another crucial detail. The phase shift that produces phase modulation in the AD9834 is the same at the fundamental output frequency as for all the other aliased carriers (see Fig.3). That is entirely different from the traditional phase modulators and transmitters described in reference books, those early FM broadcast transmitters, and the really old, sorry, ‘legacy’ 2m VHF ham transmitters. These traditional transmitters used a series of frequency multiplier stages to generate the required VHF carrier siliconchip.com.au AD9834 phase modulation details As phase deviation is proportional to both the frequency and amplitude of the modulating signal, the following equation can be used: Frequency deviation (in kHz) = phase shift (in radians) × modulation frequency (in kHz) For example, if the modulating signal’s frequency is 1kHz and we have a carrier phase shift of +½ radian, the resulting output signal’s frequency deviation is +500Hz (note that 2π radians = 360°). A standard signal generator setup for testing a 2m amateur radio VHF FM receiver (25kHz channel spacing) uses a 1kHz test tone and a carrier frequency deviation of ±3kHz. Therefore, we require a maximum phase shift on the AD9834 output carrier of 3kHz ÷ 1kHz = 3 radians. The 12-bit Phase Register in the AD9834 generates a phase shift (on the DDS output carrier) of π radians when PHASEREG = 2048. Therefore, to achieve 3 radians of phase deviation, the Phase Register must be loaded with a peak value of 3 ÷ π × 2048 = 1956. The 1kHz internal oscillator delivers a 3.7V peak-to-peak sinewave to the micro’s ADC0 analog input. This gives a peak ADC value in the 10-bit ADC register in the ATtiny45 of about 750. The ADC reference voltage is 5V, so 5V at the ADC input would result in a maximum reading of 1023. The software scales this 750 input value to give a peak Phase Register value of about 2250. That is a little higher than the calculated value of 1956 due to rounding errors in the simple integer calculation routine used. Tests with a professional-grade modulation meter confirmed this value produced ±3kHz deviation in the AD9834 output signal. If you use the external modulation input in this design, the maximum frequency deviation that can be achieved is about ±4.5kHz. This is due to the ADC measurement limit of 1023 (because of the 10-bit ADC in the ATtiny45) with a 5V peak-to-peak audio input. That input level must not be exceeded, or the ATtiny45 could be damaged. (before the arrival of phase-locked loops [PLLs]). A typical early 2m VHF ham transmitter might have a 12MHz crystal oscillator followed by a series of multiplier stages. They usually used a frequency tripler stage followed by two frequency doublers to multiply the oscillator frequency by 12, giving a final output at 144MHz. Consequently, the frequency deviation measured at 144MHz was twelve times that at 12MHz. That was very useful because these legacy phase and frequency modulators could not be phase-shifted (or frequency-­ shifted) very much. But, since the transmitter’s multiplier stages also multiplied the phase and frequency modulation deviation, the final output readily achieved the desired modulation deviation. It’s a different situation with a DDS. If AD9834 output (fout) is set to 14MHz, changing the Phase Register values appropriately in the AD9834 will produce a 1kHz tone with a 3kHz frequency deviation on that output. The 146MHz alias product will have an identical 3kHz frequency deviation due to the aliasing process in the DDS. Australia's electronics magazine There is no ‘multiplication effect’ like that in those traditional PM and FM transmitters. The alias outputs are all directly generated equally and simultaneously by the DDS NCO process. Furthermore, the AD9834’s phase modulator is a 100% digital process carried out in the NCO. The maximum frequency deviation is limited by the Phase Register length and the NCO process. The accompanying panel titled “AD9834 phase modulation details” describes how the Phase Register values generate the desired PM (and FM) deviation. Circuit details Fig.6 shows the circuit of this compact 2m FM Test Generator. The AD9834 is controlled by an Atmel/Microchip 8-pin ATtiny45 microcontroller using a three-wire SPI serial bus. The ATtiny45 has a hardware SPI interface, simplifying the software and increasing data transfer speed. This SPI interface only uses two (USCK and DO) of the usual three SPI lines because no data needs to be read from the AD9834. October 2023  47 The ATtiny45 is clocked at 16MHz using its internal RC oscillator and PLL. That releases all six I/O pins for this design (the other two are the 5V power supply). Practically all of the firmware operates using a series of software interrupt routines. Three pushbuttons (S1-S3) control the generator’s frequency and modulation. These all connect to pin 2 of the ATtiny45. Pressing any button triggers a software interrupt routine that measures the voltage at that pin to determine which button was pressed. The Frequency button (S2) allows the selection of one of eight fixed channels at 500kHz intervals from 144 to 148MHz. The Memory button (S3) selects one of four user-­programmable channels in the 144-148MHz range. Finally, the Modulation button (S1) turns the 1kHz modulation tone on and off. As described in the panel, this produces a frequency deviation of ±3kHz. A modified interrupt routine could support a rotary encoder for multi-channel frequency tuning, memory selection and other features. However, without a suitable display – there are just not enough pins – the design was intentionally kept ultra-simple and inexpensive. Generating a test tone The internally-generated 1kHz modulation test tone is produced by ‘bit-banging’ digital output pin 5 (PB0). Usually, one of the ATtiny’s internal timers would be used to do this. However, that wasn’t possible here because the timer-related pins were already handling the AD9834 SPI control bus. The bit-banging process produces an unusual low-harmonic PWM output. It is designed to null the 5th and 7th harmonics. As a result, it only requires a very modest 10kW/22nF RC filter to give a remarkably clean and accurate 1kHz sine wave. The sinewave measures around 3.7V peak-to-peak (with Vcc at 5V) when it arrives at the ATtiny45’s ADC0 input on pin 1. The 1kHz PWM tone is generated continuously at pin 5. However, it is only sampled (after the RC filter) at pin 1 with the ATtiny’s analog-to-­digital converter (ADC) when modulation is required. The sinewave’s amplitude is sampled 8000 times each second (8ksps). These samples are used to update the Phase Register in the AD9834. The relationship between the audio tone’s amplitude and frequency and the DDS-generated frequency deviation is explained in the panel above. The ±3kHz deviation for FM gives the usual 60%-of-peak-modulation Fig.6: two small chips and a handful of passive components are all that’s required in this high stability digitally modulated 2m FM Test Generator. Alignment just involves adjustment of the bandpass filter for maximum output. 48 Silicon Chip Australia's electronics magazine siliconchip.com.au level used for testing 25kHz VHF FM channels. By making this modulation process external to the ATtiny45, external modulation sources can also be used. If external modulation is selected with S4, the maximum input level of 5V peak-to-peak will produce at most ±4.5kHz deviation. For those using 12.5kHz FM channels, an external audio level of 3V peak-to-peak will give ±2.5kHz deviation with the Test Generator (peak deviation), and 2V peak-to-peak will give ±1.75kHz deviation (60% of peak deviation). Those figures all assume Vcc is close to 5V. The 8kHz sampling rate used in this design limits the modulating frequency to less than 4kHz (the Nyquist limit). However, the lack of any anti-aliasing filter in the software practically limits external modulation frequencies to less than 3kHz. Output signal generation An 80MHz external crystal oscillator clocks the AD9834. This frequency is close to optimal for this application because it eases the RF filtering task slightly, and suitable crystal oscillators are readily available at low cost. As described earlier, a low-loss, highly selective bandpass filter is required to extract the wanted super-Nyquist 2m-band RF signal. A pair of high-Q air-wound inductors are used. These are essential to produce the desired result. The filter is designed to give about 40dB of attenuation at the nearest alias bands close to 100MHz and 200MHz while introducing no more than 4dB passband loss. Happily, these inductors are quick and easy to make at minimal cost. Despite the wide variation in output levels generated by the DDS process, the resulting 2m band output levels (post-filter) are about -40dBm ±2dBm. The directly generated carrier, the residual clock and the other aliases are attenuated by 25dB or more, and spurious products are at least 30dB below the output level. A pair of switched attenuators provide three output levels suitable for receiver tests. The highest output level, -45dBm ±2dBm, places an FM receiver well into limiting without overloading, producing a 1kHz demodulated audio tone with a very good signal-to-noise ratio. siliconchip.com.au Enabling one attenuator (either) gives a signal level of about -75dBm. This is close to the typical ‘corner’ of FM receiver performance where limiting begins to improve the receiver’s signal-to-noise usefully. Adding the second attenuator gives a test signal of about -105dBm. This is close to that used in typical 12dB SINAD receiver sensitivity and squelch gating tests. The absolute accuracy of these levels depends in part on the output filter alignment and the construction method. The prototype was housed in a 3D-printed enclosure, which provides limited shielding. That limits the absolute accuracy of the signal level and the absolute accuracy of some measurements, so if you’re after precision, you will need a metal case for shielding. Power supply My initial plan was to derive the 5V supply for the ATtiny45 and AD9834 using a 7805 linear regulator. While the AD9834 data sheet states it is a “low current DDS device” (20mA at 5V), it needs an external clock generator, in this case at 80MHz. These typically consume 30-70mA, although a few will operate with as little as 10mA. Hence, a 78L05 might not be sufficient when operating from a 9-12V DC supply. An alternative is to use a switchmode regulator module like the one shown in Photo 1. This can be mounted in place of the 7805 linear regulator on the PCB. The input voltage can be from 6V to 15V DC, and the 5V output can deliver up to 500mA. It improves efficiency and remains cool during operation. The prototype is powered by a single 1.5V AA alkaline cell. This is only suitable for intermittent use due to the limited capacity of the cell but allows a compact 3D-printed PLA enclosure to be used. A boost regulator module steps the cell voltage up to 5V (shown in Photo 2). Finally, powering the Generator from a single Li-ion or LiPo cell is also possible. They have a nominal fully charged output voltage of 4.2V and an operating end-point voltage of 3.5V. I tested the Generator with supply voltages from 3-5V. The output level remained constant within 0.2dB across that voltage range! If using a Li-ion or LiPo cell, there is also the option to integrate a small Australia's electronics magazine USB charger PCB (see Photo 3). Some versions include an automatic battery disconnect feature to ensure the battery does not operate below 3.5V, which could damage it. Construction The Test Generator is built on a small 50 × 70mm PCB, coded 06107231, that hosts a mix of SMD and through-hole parts. The board has a near-­ continuous top-side ground plane with all the SMD parts mounted on the underside. This arrangement keeps the unit compact while allowing for easier testing and modification during development. It also produced improved RF performance over other approaches. The layout is shown in Fig.7. Start by fitting the 23 SMD components on the underside. It is easiest to start with the AD9834. Position it over its pads, tack one lead, then double-check that its pin 1 orientation is correct and all pins are correctly centred on their pads before soldering the rest. Adding a little bit of flux paste to the pads and on the leads will make soldering it much easier. If you accidentally bridge any of its pins (which is easy to do), add a bit of Photo 1: a DD4012SA small switching buck regulator (top and bottom shown) can deliver 5V DC to run the chips efficiently. Photo 2: this tiny 5V boost regulator module is used to step up the cell voltage. Photo 3: this TP4056 module charges a Li-ion or LiPo cell and automatically disconnects the load if the terminal voltage falls too low. October 2023  49 bit, scrape the enamel from the wire ends to allow for the soldered PCB connections. Flip the board over and continue construction by adding the ATtiny45’s socket (watching its orientation), the two trimmer capacitors, the two inductors and the two electrolytic capacitors on the top side of the PCB. Now mount the crystal oscillator module. The PCB allows for either full or half-sized oscillator modules to be used. Next, install the three pushbuttons, the two slide switches, the toggle switch, and finally, the regulator (a 7805 or one of the other options). 144MHz to 148MHz. Enter your choice of frequencies in the blue cells. It’s best not to touch anything else! After entering the four memory channel frequencies into the spreadsheet provided (left side of Screen 1). Scroll down to the bottom of the worksheet and click on the green Write EEP File button (Screen 2). The spreadsheet then generates and saves the 2mTestGenFreq.EEP file in the same directory as the spreadsheet file. If you don’t have Excel, you can open the file in a free package like LibreOffice, and everything will work except for the final file-saving step; pressing the green button will do nothing. Instead, after updating the frequencies, check the text just to the right of that button. You will see three lines that start with colons. Click your mouse on the left side of the first line that starts with a colon (just to the right of the colon), then drag it down to the third line and release the button. Press CTRL+C (or the equivalent command to copy to the clipboard), then create a new text file, open it and press CTRL+V (to paste those lines into it). Save that file and then rename it from a .txt extension to .eep. That gives the same result as Excel does when pressing the button. Either way, rename the resulting EEP file so you know what it’s for. Otherwise, the next time you use the spreadsheet, it will overwrite your previous file. Generating the EEPROM file Programming the ATtiny45 I have created a spreadsheet to allow the easy entry and programming of the four user-selected 2m frequencies. These may be on any frequency from The HEX file for the Test Generator is available for download from the Silicon Chip website, along with the BASCOM source code. You can Fig.7: the Test Generator is built on a compact 50 × 70mm double-sided PCB with SMDs on the underside and the through-hole components on the top. flux paste to the bridge and apply some clean solder wick with your soldering iron. Once it gets hot enough and the flux starts to smoke, the excess solder will be pulled into the wick, leaving clean solder joints without a bridge. Repeat as necessary until all the solder joints look good under magnification. The remaining SMDs can then be fitted. All can be soldered in place by hand with a fine-tipped soldering iron. Fit the edge-mount SMA coaxial connector after that. Make the two inductors using 0.4mm diameter (26SWG) enamelled copper wire wound on a 5mm diameter drill bit shaft. Close-wind 10 turns for each, then stretch each coil slightly until each measures 13mm long. Allow 10mm of extra wire at each end of each coil for the connections. While keeping each coil on the drill Fuse settings for the ATtiny45 1. Memory Frequency Tables – ENTER YOUR FREQUENCIES HERE 2m TG Frequency Data Ch 01 144,285,000 Ch 02 145,775,000 Ch 03 146,900,000 Ch 04 147,250,000 HEX EFCAB8 D90E68 C7E3E0 C28CB0 Enter your four memory frequencies in the BLUE cells Calculated HEX value B8 68 E0 B0 EEPROM Data CA EF 0E D9 E3 C7 8C C2 00 00 00 00 INSERT MEMORY FREQUENCIES HERE Byte Value Lock byte 0xFF Extended 0xFF byte Four bytes of data per frequency to be stored in the EEPROM Screen 1: a shot of the spreadsheet which is used to generate the data required to program the user-selected 2m frequencies. High byte 0x57 Low byte 0xE1 Click on this button AFTER you have entered all four frequencies into the cells in Section 2 above Write EEP File Screen 2: clicking on the green button automatically generates the ATtiny45 EEP file, which contains your four desired frequencies. 50 Silicon Chip Notes Australia's electronics magazine RSTDISBL = 0 (set), EESAVE = 0 (set) CKSEL = 0001 for 16MHz internal RC oscillator, CKDIV8 = 1 (disabled) siliconchip.com.au load the EEP file with the four user-­ defined frequencies into the chip at the same time. Program your ATtiny45 with the HEX and EEP files using a suitable programmer (USBasp etc). After that, program the configuration fuses. Table 1 (“Fuse settings for the ATtiny45”) shows the required fuse settings. My article on the Shirt Pocket DDS Oscillator in the September 2020 issue included a small programming adaptor that can be used to program an ATtiny chip out of the circuit in conjunction with a suitable serial programmer (see p47; siliconchip.au/Article/14563). The PCB is still available from the Silicon Chip Online Shop; see siliconchip. au/Shop/8/5642 You could also use our May & June 2012 PIC/AVR Programming Adaptor (siliconchip.au/Series/24) or build an adaptor on a breadboard or small piece of protoboard. Reprogramming the ATtiny45 If you want to change the memory channel frequencies, you can’t just put the chip back into a regular programming adaptor since the RESET pin is disabled. The ATtiny45 must first be erased using a special HV programmer. I have designed a simple chip eraser and fuse restorer (“CEFR”) to do this. You can read about how to build it on my website at www.zl2pd.com/CEFR_ Fuse_Reset_Tool.html – it requires no special parts and can be powered from a USB socket or external 5V USB power supply. Another well-known DIY fuse resetting tool is the Fuse Doctor (see https://github.com/SukkoPera/ avr-fusebit-doctor). Final assembly Depending on the enclosure and Parts List – VHF / FM Test Signal Generator 1 double-sided PCB coded 06107231, 50 × 70mm 1 3D-printed case & front panel label 1 set of AA cell contacts 1 AA alkaline cell 1 80MHz crystal oscillator, full or half-size DIP type (X01) [AliExpress siliconchip.au/link/abmb] 3 PCB-mount momentary tactile pushbutton switches (S1-S3) [Altronics S1126A, Jaycar SP0609] 4 solder tag miniature DPDT slide switches (S4-S7) [Altronics S2010, Jaycar SS0852] 1 8-pin DIL IC socket (for IC1) 1 SMA edge connector (CON1) 3 2-pin headers, 2.54mm pitch (optional) (CON2-CON4) 1 3-pin right-angle header, 2.54mm pitch (if REG1 has none) 2 No.4 × 5mm self-tapping screws 2 M3 x 8mm panhead machine screws 2 M3 x 8mm countersunk head machine screws 2 10mm-long M3-tapped Nylon spacers 1 400mm length of 0.4mm diameter/26SWG enamelled copper wire (for L1 & L2) [Altronics W0404, Jaycar WW4014] various lengths of light-duty hookup wire Semiconductors 1 ATtiny45-20PU 8-bit microcontroller programmed with 0610723A.HEX, DIP-8 (IC1) 1 AD9834-BRUZ or -CRUZ DDS signal generator IC, TSSOP-20 (IC2) [AliExpress siliconchip.au/link/abmc] 1 3-pin 5V output boost module (REG1) (for AA cell operation) [Silicon Chip SC6780, AliExpress siliconchip.au/link/abmd] OR 1 3-pin 5V output buck module (REG1) (for 6.5-40V DC operation) [Silicon Chip SC6781, AliExpress siliconchip.au/link/abme] OR 1 7805 5V 1A linear regulator, TO-220 (for 8-16V DC operation) Capacitors (all SMD M2012/0805 50V ceramic unless noted) 1 10μF 50V/63V radial electrolytic [Altronics R5065, Jaycar RE6075] 1 1μF 50V/63V radial electrolytic [Altronics R5018, Jaycar RE6032] 5 100nF X7R 1 22nF X7R 1 10nF X7R 1 120pF NP0/C0G 2 47pF NP0/C0G 2 6-20pF PCB-mount trimmer capacitors (VC1, VC2) [Altronics R4005] Resistors (all 1% SMD M2012/0805 size) 2 10kW 1 6.8kW 1 3.9kW 1 1.8kW 2 820W 4 51W 1 220W Photo 4: my simple Chip Eraser and Fuse Restorer (CEFR) resets ATtiny25/45/85 fuses back to the factory default settings so that you can change the memory channel frequencies. Parts availability We don’t have a kit for this project but we can supply the PCB, programmed microcontroller and buck or boost module. The remaining parts can be found at your usual suppliers or from the sources listed above. October 2023  51 Photo 5: the PCB fits in a 3D-printed enclosure and is powered by a single 1.5V AA cell. The boost regulator module is to the left of the power switch, while the output filter is above and alongside the regulator. The AD9834 and other SMD parts are on the underside of the PCB, but their locations are marked on the component side. power supply option you select, add the power switch and power wiring to suit. In the prototype, the AA cell is located in the lower part of a 3D-printed case designed for the board. STL files for the enclosure are available for download along with the software, see siliconchip.com.au/ Shop/6/266 The ‘battery shrapnel’ (those metal tabs at each end of the battery compartment) slide into the slots designed for them, and the power switch likewise slots into place in the case. The PCB can then be mounted. Two 5mm-long, 3mm diameter self-tapping screws pass from the underside into two 6mm-long Nylon spacers to hold the PCB in place. Four more screws hold the front panel in place from the front. Testing and operation Insert the programmed ATtiny45 into the socket, ensuring its pin 1 end is at the notched end of the socket; if in doubt, check Fig.7. Switch both attenuator switches on the Test Generator to the left-most positions (minimum attenuation). Place a 2m VHF FM handheld within about 500mm of the assembled PCB and set it to receive on 146.000MHz. Unmute the receiver so 52 Silicon Chip you can hear channel noise and adjust the volume to a suitable level. Connect and turn on the power to the Test Generator. The handheld’s receiver should immediately go quiet, and the handheld’s signal strength meter (if there is one) should indicate a very high level (S9 or better, typically). If this does not occur, turn off the power and carefully check your construction. Assuming your Test Generator passed this test, briefly press and release the Modulation button. You should hear a clean 1kHz tone in the FM handheld’s speaker audio. While monitoring the audio and observing the handheld’s signal level meter, adjust the two trimmer capacitors on the Test Generator to achieve the maximum signal level. You might need to move the handheld several metres away (or more) so you begin to hear a little noise on the received signal. A slight improvement in tuning can sometimes be achieved by very slightly compressing or stretching one or both of the coils, but this is seldom necessary. The generator starts with the output set to 146.0MHz without modulation. Each press of the Frequency button increments the frequency by 500kHz. If the current frequency is 148.0MHz, the next press will change the output to 144.0MHz, and the 500kHz frequency steps resume again through the 2m band. Briefly press the Frequency button once to change the Test Generator to 146.5MHz. Retune the handheld’s receiver frequency to 146.5MHz; the modulated signal should be audible on this channel. Press the Modulation button briefly to verify that the modulation can be turned on and off as desired. Ensure What about phase modulation? You might have noticed I wrote about phase modulation, but the design only supports CW or FM. So what’s going on? Phase and frequency modulation are two sides of the same ‘angle modulation’ coin. If a modulator is a true phase modulator, the input audio signal is integrated before modulation to produce FM. Likewise, differentiating the input signal to a genuine frequency modulator results in phase modulation. Hams (amateur radio operators) all talk of “FM”, regardless of how it’s generated in their radios. When using analog angle modulation (“FM”), it was also always easier to measure frequency deviation when setting up transmitters and everything associated with them. Nobody ever measured phase shift. So everyone talks about FM and frequency deviation when talking about analog angle modulation. More importantly for the 2m Test Generator is that, for a single tone, FM and PM are indistinguishable. Curiously then, but logically in context, we only talk about (and measure) specific instantaneous phase shifts when it comes to data angle modulation. Hence PSK, QPSK and 8PSK, where we see a digital application of relatively large phase step modulation. You might recall that I mentioned the possibility of AM. Not many folk use AM on 2m, but interestingly, combining AM and PM makes it possible to generate 16-QAM with a modest amount of extra effort. But that is an idea for another day. Australia's electronics magazine siliconchip.com.au modulation is on again before proceeding to the next test. If the Memory button is pressed, the generator will deliver one of four programmed frequencies starting with the first memory channel. Pressing the Frequency button will return the oscillator output to the currently selected 500kHz frequency increment. Change the handheld receiver frequency to the frequency you programmed as Memory Channel 1 by pressing the Memory button briefly. The modulated signal should now appear on this channel. You can continue to press the Frequency or Memory buttons to select and test the other Generator frequencies. Important notes Signals generated on some frequencies can produce spurious in-band and out-of-band products. This is to be expected from such a simple DDS generator. Analog Devices warn about this in the data sheet, too. These additional signals on the output can be generated by the DDS clock, its harmonics and the mixing of one or more aliases. They are typically at least 25dB (aliases) or 30dB (spurious) below the desired output. That’s similar to a few legacy commercial RF signal generators. Given the absence of anti-aliasing audio filtering, avoid the temptation to feed microphone audio into the external audio input or to add a low-power RF amplifier to the Test Generator. It is not suitable for use as a 2m FM transmitter. While usable for basic testing, it will not meet any regulatory test standards for FM transmitters. External modulation You can use an external audio source, such as an audio oscillator, to modulate the Test Generator. This can be applied to the CON2 input on the PCB. Ensure the level is between 0V and the supply voltage (ie, 5V maximum with a 5V DC supply). That means the signal must have a ~2.5V DC bias. Signals beyond that limit can cause damage. Monitor the output on a nearby 2m handheld transceiver or receiver to confirm that the modulating tone can be heard. If you want to add a socket to feed in an external modulation signal, we suggest you couple the signal from that socket to CON2 via a 100nF capacitor and connect 100kW resistors from the CON2 signal pin to 5V and GND points on the PCB to get the correct biasing. CTCSS operation A suitable CTCSS encoder can also be connected to the CON4 CTCSS input on the PCB. This may be used, for example, to test an FM receiver’s CTCSS decoder. To do this, set the handheld to a suitable channel and set the handheld CTCSS decoder to an appropriate Fig.8: the front panel graphics can be printed and laminated, then glued to the front of the case. CTCSS frequency, eg, 123.0Hz. Ensure the CTCSS encoder’s maximum output level is no more than about 0.5V peak-to-peak. Select internal modulation as the source on the Test Generator, and push S1 briefly to turn on the FM modulation. When the external CTCSS encoder is operating, the receiver’s CTCSS decoder should detect the CTCSS tone, unmute the receiver, and the Test Generator’s 1kHz tone should be heard. Turning the external CTCSS encoder off or reducing its level below about 0.1V peak-to-peak should cause the receiver’s CTCSS decoder to mute the receiver audio. However, CTCSS decoders can be very sensitive and may continue to detect a valid tone with CTCSS tone input levels of even 5mV peak-to-peak! Final comments Photo 6: the underside of the PCB with all the SMDs fitted. The bridged pins (9 & 10) on the AD9834 chip are both joined to GND, so I left it like that. siliconchip.com.au Australia's electronics magazine The difficulty I encountered in finding basic information and application examples on DDS phase modulation surprised me, given that the data sheets heavily promote this feature. However, achieving precise phase (and frequency) modulation levels with the AD9834 ultimately turned out to be relatively simple. I hope you find the details and design to be of interest. This compact FM Test Signal Generator is fun to use and a great conversation piece. SC October 2023  53 Linshang LS172 Colorimeter If you want to find a paint colour that matches your existing paint or verify that batches of products you are ordering have matching colours, this device is perfect. It’s relatively inexpensive, very accurate and quite easy to use. It even costs less than a single colour sensor we recently looked at! Review by Allan Linton-Smith T he LS172 is a hand-held colorimeter that’s ready to use out of the box. It is capable of accurate measurements and allows you to easily compare the colours of different objects. It uses reflected light from a LED beamed onto a sample, analysing colour and intensity. It is an essential tool for anyone involved with colour measurement, such as painters, decorators, or anyone requiring standardisation of coloured items. It gives you CIELAB (L*a*b*) measurements (when translated from French to English, CIE stands for the International Commission on Illumination) and can also measure tiny colour differences. Additionally, it can convert colour values into Pantone numbers, which printers and colour consultants often refer to. It costs around $250-300 depending Background image: https://unsplash.com/photos/46juD4zY1XA on where you buy it; it is available from eBay, Amazon, AliExpress and other online retailers. That might sound expensive, but it’s cheap compared to what was available before! For comparison, the Omron BW5C colour sensor can be purchased from DigiKey for around $280. And that’s just for the sensor! The LS172 is undoubtedly good at matching house paint; I recently used it to match my house colour to a colour sample at the hardware store. I used its memory to store my house colour CIELAB measurements. I then checked out similar colour sample cards until it gave a “green” reading, indicating that the sample was almost identical to the house colour. The colour it identified was “Beige Royal”, which it indicates is similar to Pantone 7527 C or Pantone 7434 C. It LS172 Features & Specifications » » » » » » » » » » » » 54 Illumination: full-spectrum LED, 45° annular illumination, 0° viewing angle Measuring aperture: 8mm, 10° field of view Measuring time: about one second Colour standards supported: CIELAB, Pantone, Luv, LCh, Yxy, CMYK, RGB, Hex Colour difference formulas: ΔE*ab, ΔE*uv, ΔE*94, ΔE*cmc(2:1 or 1:1), ΔE*00 Standard deviation for ΔE*ab: ≤ 0.03 (average of 30 white tile measurements three seconds after calibration) Dimensions: 86×62.5×158mm, 225g Power supply: rechargeable 3.7V 4000mAh Li-ion cell; 10,000 measurements from full charge Display: 480×320 pixel IPS colour LCD screen Charging port: Type-C USB Operating conditions: 0-45°C, 0-85% relative humidity (no condensation) Language support: English, Simplified Chinese Silicon Chip Australia's electronics magazine also tells me that Beige Royal is ‘more white, slightly more red and slightly more blue’ than my house colour. The device can store 1000 colour measurements, so you can keep your kitchen, bathrooms and other samples for reference if you want! The hardware store I went to has a colour-matching system but no CIELAB reference or Pantone numbers, meaning I would have to chip off a bit of paint from my house to match it. I much prefer using the LS172 to damaging the house! Note that smartphone photos are not good enough to match colour accurately because of lens filtering and light source variations, which can easily shift the colour and intensity and result in an imperfect match. There’s also no guarantee that a phone camera has a wide enough colour gamut to distinguish all colours the human eye can. The CIELAB colour space The L*a*b* numbers represent any colour and its brightness with three coordinates. The L value indicates the brightness, with 100 being pure white and 0 pure black. The other two values, a & b, represent the colour’s hue and saturation, ranging from -128 to +128. They are the x & y coordinates on a standard colour chart, shown in Fig.1. Note how the centre is unsaturated (grey) and colour saturation increases as you move towards the circle’s circumference. siliconchip.com.au Therefore, the a & b coordinates encode both the shade (hue) and colour intensity (saturation). Adding L (brightness) gives you everything you need to define a colour. The entire colour space approximates the range of human daylight vision. I measured the yellow lid of a Vegemite jar, which was indicated as L=71.6, a=7.8, b=87.4. Interestingly, using the LS172 to compare the lid to the label, it said they did not match and that the label was “more white, more green and more blue”, even though it looked identical to my eyes! You can find more details on L*a*b* colours at https://w.wiki/7GRT Using it The LS172 is really easy to use. All you need to do is place it on a flat item such as a wall, door or colour card you wish to match. You can then store its colour as the “standard” and compare it to various samples later, to find a match or determine exactly how different they are. A typical screen image during use is shown in Screen 1. It calculates the delta (difference) between your standard and your sample and tells you if you pass or fail with a green or red background to the delta bar. There are various options for calculating the delta estimate; we used the standard “ΔE*ab”. You can also change the delta threshold that determines its sensitivity to differences. As mentioned above, it gives you the delta figures and human-readable text like “more blue” or “more yellow” etc. This can be handy since, as I wrote, they often look identical to the eye. If you were mixing paint, you could use those hints to add a small amount of extra tint to end up with a spot-on mixture. The LS172 calibrates instantly using the little tile in its protective cover and requires no external calibration. It is easily recharged with a USB-C charger and you can just put it in your pocket or handbag (although it’s a bit chunky to carry comfortably in our pockets). Its built-in rechargeable Li-ion battery is claimed to be good for 10,000 measurements with a full charge. It has a user-friendly 3.5-inch (89mm) diagonal touch screen and can quickly match the closest Pantone colour number with a claimed accuracy above 90%. One of the excellent practical siliconchip.com.au features is the on-screen retention of the saved colour; the comparison colour is also saved in a split screen for easy reference. b+ How is it? In summary, the LS172 is a cost-­ effective tool for those involved in colour specifications, colour analysis and colour control. It is a versatile a− instrument with an excellent memory and can quickly be set up for various analyses. For more information, visit the manufacturer’s website at siliconchip.au/ link/abpi Finally, the Editor had a good b− question: what if you want to match a metallic finish, like many automo- Fig.1: a ‘slice’ through the L*a*b* tive paints? I guess the answer is that colour space at around L = 50, halfway between white and black, it would require a different type of giving a neutral grey shade in the instrument; after all, no instrument centre. The example coordinates can do everything! shown here, a = 55 & b = 40, give a A bit of history Early colour measurements and colour matching were done with pretty crude devices such as a “colour comparator”, a circular dial of various colours that you put against a sample. When it matched by eye, you noted the colour number on the dial. However, it rarely matched perfectly! For liquids, we used “standardised nestle” tubes, large test tubes of exact dimensions that we held up to daylight to compare with a sample of a previously standardised product. These methods relied on subjective evaluations and depended on the light source and human judgement. Tungsten light can easily hide colour differences; the LS172 uses pure white light from its LED source. Also, not everyone has perfect colour vision. Where I worked, an Ishihara test was given to laboratory staff before any colour decisions could be made. Approximately one in 12 males and one in 200 females are colour-blind. You can take the test yourself at www.colormax.org/color-blind-test/ The origin of CIELAB Richard Hunter developed colorimeters and the L*a*b* system in the 1950s to quantify exact colour hues and intensities using numerical values determined by reflected light. Hunter’s colorimeters were first used commercially by Proctor & Gamble to accurately standardise the colours of Australia's electronics magazine peachy colour. As this is circular, √a2 + b2 ≤ 128. Since the magazine is printed in CMYK, this figure will not be displayed accurately. Source: https://chromachecker.com/manuals/ en/show/chromaspot Screen 1: the main screen during use. You can see the measured L, a, b, C & h values at top middle in blue, with the reference values in black to their left. The differences are shown to the right and summarised in the green bar just below the middle of the screen. The perceptual differences are shown on the right. C is for chroma and h is for hue. October 2023  55 a+ Left: a Gardener Laboratory L*a*b* Colorimeter and power supply weighing around 20kg (owned by the author) compared to the LS172. The LS172 is smaller and lighter than the laboratory unit’s colour sensor head! Below: here is the LS172 measuring the colour of a pink sheet. The device provides multiple matches of different Pantone colours. The LS172 also includes a “calibration tile” as part of the bottom cap, which is shown inset. This tile is used as a white reference during calibration. their soaps. The giant company Dow then adopted them to measure and standardise plastics. I was fortunate to meet Richard many years ago and was delighted to play around with one of his early colorimeters. Convinced that it would be a game changer in the R&D lab where I worked, I put in a request to get one. I wanted to numerically standardise tomato paste, tomato sauce and various fruit concentrates to ensure consistent quality and help select the best raw materials. However, the response I got was, “$8,000 for that! Can’t you just use your eyes?” Most serious food labs now have such a colorimeter. The photo above shows my Gardener XL-800 Series display plus XL-825 Optical Remote Sensor Colorimeter. It operates only from 110V AC, consuming over 600W, so it requires a huge 230V to 110V stepdown transformer. It is now obsolete and destined for a museum; a decision I made after testing the little LS172! Richard Hunter told me that he sold many instruments to forensic labs to compare paint fragments for motor vehicle “hit and run” cases; his instruments were so sensitive that they were able to match paint chips What is Pantone? Pantone is a proprietary colour-matching system developed by the company Pantone LLC. Individual colours are named and matched to a specific printing process (called the Pantone Matching System), with the type and quantity of ink or pigment used cross-referenced to their name. The importance of Pantone colours comes from the accurate reproduction and standardisation. This means that no matter the location, a specific Pantone colour will display and be printed exactly the same (assuming the printer follows the standard). It’s common for logos to be specified using Pantone colour(s), so that no matter if it’s printed on a metallic can, wooden box or piece of paper, it will look the same. 56 Silicon Chip Australia's electronics magazine on victims to the exact offending car because no two cars are exactly the same colour! Evidence with L*a*b* measurements is now accepted in most courts. Spectrometers were also used (and still are) to display colour spectra absorbance of liquids vs wavelength in nanometres over the visible range. However, such measurements require expert interpretation, and you need a large data bank of standard colour spectrograms for comparison. Early colorimeters such as the Gardener were very heavy, used a lot of power and were consequently restricted to bench work. They were also difficult to calibrate. Editor’s note: while the spelling “colourimeter” is sometimes used (along with “colourimetry”), it is not common. In Australia, we find it mainly referring to a different type of instrument that measures chemical concentrations by absorption of specific light wavelengths. Therefore, we are using the spelling ‘colorimeter’, even though it might appear inconsistent with the typical Australian spelling of similar words. SC siliconchip.com.au Build It Yourself Electronics Centres® It’s a new catalogue ! n o i t a r b e Cel value savings | Shop in store Latest release deals & great or online. SAVE $50 NEW! 54.95 $ 1000’s sold! r Top choice fo enthusiasts & trade 145 $ T 2631 NEW! 129 $ D 0520 65W Portable Laptop Battery Bank Stay charged. Stay on time! Surprisingly compact 20,000mAh battery bank with USB PD over 65W for large laptops! Features 2 PD outputs and 2 QC3.0 outputs for simultaneous charging. Ok for air travel. A stylish bedside or desktop alarm clock with in-built 15W wireless charging for your phone & FM radio. Display also shows calendar and temperature. 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Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0010 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Mini inverter to power a soldering iron This simple but inexpensive inverter can power a small soldering iron (eg, 25-35W) in the absence of a mains supply. It uses eight transistors and a few resistors and capacitors. NPN transistors Q1 and Q2 (BC547) form an astable multivibrator that produces a 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to a PNP Darlington driver stage formed by transistor pairs Q3/Q5 and Q4/Q6. The outputs from the drivers feed NPN transistors Q7 and Q8 (2N3055) for push-pull operation. Q7 and Q8 need heatsinking. A 230VAC to 9-0-9V AC, 100VA transformer (T1) is used to step up the voltage from Q7 & Q8 to close to 230V AC. The centre-tapped terminal of the ‘secondary’ of the transformer (actually the primary here) is connected to the battery (12V, 7Ah), while the other two terminals of the ‘secondary’ connect to the collectors of power transistors Q7 and Q8. When you power the circuit using switch S1, transformer T1 produces 230V AC at its ‘primary’, although it will be higher without a load. This voltage can be used to power your soldering iron. If building this circuit, it must be housed in a suitable enclosure (Earthed if it’s made of metal) with correctly-rated, insulated wiring and a proper mains output socket. For countries that use 110-120V AC, all that needs to change is the output transformer, which should have a suitable ‘primary’ voltage. Raj. K. Gorkhali, Hetauda, Nepal. ($75) Editor’s note: small modified square wave 12V DC to 230-240V AC inverters are inexpensive and safe, with the correct peak voltage and RMS voltage output. We recommend using one of those and are presenting this circuit mainly because it’s interesting. VR1 & VR2 should be set at mid-way and then adjusted for 50Hz operation. Improved gesture recognition software You may recall that in the article on the CJMCU-7620 Gesture Recognition Module in the March 2022 edition of Silicon Chip (siliconchip. au/Series/306), major difficulties were experienced trying to interface it with a Micromite. To try and overcome these, it was powered from 3.3V rather than 5V (for reasons that could not be explained), but it was still somewhat temperamental. I downloaded and modified the original code from the Silicon Chip website. It now works perfectly with a 5V supply. It will also work on both siliconchip.com.au the Micromite and PicoMite without modification. I made many changes to the original program; the main two that got it working were new initialisation parameters and removing all the “pause” statements that resulted in missing interrupts from the gesture sensor. I found a new data sheet which detailed the correct initialisation sequence (available to download from siliconchip.au/link/abmt). I replaced the ‘pause’ statements with a timer so that the program continues to poll the sensor rather than sleeping. Australia's electronics magazine I also made a small modification to improve the detection of the Wave gesture, which was initially difficult for the sensor to recognise. I have also reinstated the comments on the initialisation parameters. This final revised version of the software is available for download: siliconchip. au/Shop/6/6313 The sensor is now in the spares box as, although interesting, I am struggling to think of a use for it except perhaps as a light show driving a WS2812 8×8 LED matrix. Kenneth Horton, Woolston, UK. ($80) October 2023  61 Raspberry Pi Pico W BackPack ‘analog’ clock This primarily software-based project uses the Raspberry Pi Pico W BackPack (January 2023; siliconchip.au/ Article/15616). It is an analog-looking clock (see photo) that synchronises its time from the internet using NTP. It can be used with or without the DS3231 real-time clock (RTC) chip. It also serves a web page that allows communication with the Pico W so you can: • See the time from the Pico W in the browser and a heartbeat display (a pulsing red square) that shows the device is running. • Send a message for display on the BackPack LCD screen. • Play sounds on the BackPack from 8-bit mono WAV files stored on the SD Card. The sound quality is surprisingly good. • Set the Alarm time on the BackPack and display the event on the browser when triggered. Constructors could add external circuitry to do something when the alarm triggers. The code can be easily expanded by the reader using the Arduino IDE V2. The clock display has an analog face with a second hand, plus a digital display of the date and time. Messages and events (like “Alarm triggered” or “Alarm Reset”) are displayed at the top left. The Arduino code is provided as a zip file containing everything needed to compile and upload to the BackPack, including all necessary libraries. First, format an SD Card of no more than 32GB as FAT32. Copy the supplied WAV files to the SD card, remove it as usual, and insert it into the Pico W BackPack’s slot. I used the Arduino IDE V2.0.3, which you can download from www. arduino.cc/en/software 62 Silicon Chip The next step is to select the correct target board. If this is the first time the IDE has been used with a Raspberry Pi Pico, the board repository where the details of the RP2040 processor are located needs to be added. Click File → Preferences to bring up the preferences dialog box, then click the folder icon at the right of “Additional Boards Manager URLs” and add the following URL at the end of the list: https://github.com/earlephilhower/ arduino-pico/releases/download/ global/package_rp2040_index.json Click the Boards Manager icon at the left of the IDE and enter RP2040 in the text box at the top. Select the “Earle F Philhower” version and click INSTALL at the bottom of the boards description. Copy the “libraries” folder to the Sketchbook Location; if the libraries folder already exists, just copy the supplied libraries into that folder. Open the sketch with File → Open menu item. Navigate to the Sketch folder and select the “Pico_Web_Backpack.ino” file. Next, change the “ssid” and “password” variables at lines 59 and 60 of “Pico_Web_Backpack.ino” to identify your WiFi router. Be sure the BackPack is plugged into a USB port, click “Select Board” at the top of the IDE to tell the IDE which board and USB port to use. Click “Select Other Board and Port” if the Pico W and USB port are not automatically selected. Compile and upload the code to the Raspberry Pi BackPack by Clicking the “Upload” button (the right arrow at the top left of the IDE). If all goes well, the BackPack will restart after a few minutes. The BackPack will check for an SD card and the optional RTC and then indicate it is connecting to WiFi. After Australia's electronics magazine a few asterisks are printed, and provided you have changed the code to identify your router correctly, it will show a successful connection and give the IP address for the web server. Note this, as you will need it to access the web page. A message will then appear indicating that the date and time are being synchronised with the internet (NTP), followed soon after by successful (or not) synchronisation. Finally, the analog clock face will be displayed, showing the current time along with the digital date and time. The web server will now be running and is ready to access using any standard internet browser. The web page displays the BackPack’s current date and time, updated every second. The red square at the top right is known as a heartbeat and ticks every second to let you know the BackPack is running. Enter a message in the text box at the top (maximum 30 characters) and click the “Send Msg” button. The message will be displayed at the top of the BackPack’s display. Select a number 1- 6 and click the “Play Sound” button to play one of the wave files on the SD Card. Connect powered desktop speakers to the BackPack for the best sound quality. Enter a desired “On” time and “Off” time in the boxes shown and click the “Set Alarm” button to send parameters to the BackPack indicating a time when the alarm events are to be triggered. The code will set a GPIO pin to high at the alarm on-time and low at the off-time. This is currently GPIO1, but it can be changed to any available GPIO pin by altering the value of the AlarmPin variable in the code. The firmware can be downloaded at: siliconchip.com.au/Shop/6/264 Dennis Smith, Strahan, Tas. ($120) siliconchip.com.au Automatic AI Doorman using a Maixduino We had an IR proximity sensor for opening the doors to our office, but people walking past in the hallway would frequently trigger it, letting the air-conditioned air out and noise in! The solution is this ‘doorman’ based on a Maixduino module which only opens the door when someone approaches it. The Maixduino is a 5V-powered Arduino-compatible module with an ESP32 sub-module with WiFi and Bluetooth, a 24P camera connector, a Sipeed M1 dual-core 400MHz RISC-V CPU with FPU and AI, and an audio interface, among other features. It costs under $50, and the camera adds about $6 more, for a total of just over $50. The Maixduino uses a camera and artificial intelligence (AI) to determine when someone walks up to the door. If it senses a person, it waits until they approach within 2.5m of the door. It then opens the door. If the person passes by without looking at it, the door will not open. The circuit is simple; GPIO pins D12 & D13 of the Maixduino control two transistors that switch 5V relays to trigger the door open and close actuators. The software is written in Micropython and takes advantage of the Maixpy ‘facedetect’ classifier, available in a file named *.kfpkg (* is the model’s name). These are highly efficient, fast-acting YOLO (You Only Look Once Version 2) classifier models. Each scene is passed through the model and the output is checked against defined classifiers. Since YOLO v2 is very fast, it immediately identifies a human face in the scene and draws a box around the face. The width and height of the encompassing box are then used to compute the person’s distance from the camera. It uses that to decide whether to open the door. For example, a face box 81 pixels wide implies a person standing 50cm from the camera, while a box 47 pixels wide means they are 1m away and 24 pixels wide means they are 2.5m away. Any smaller/further than that and it won’t open the door. The classification model used is facedetect.kfpkg. Inside the Micropython program, the model is loaded by siliconchip.com.au calling the register number inside the kpu library. “kpu” stands for knowledge processing unit. The software is available from siliconchip.com.au/Shop/6/262 and you can use the kflash_gui utility to upload the binary file to Maixduino. First, connect the Maixduino to a USB port on your computer. Load kflash_gui and then connect to the device by selecting the correct serial port. If Micropython is not already installed on the Maixduino, it is time to install it. Select the file maixpy_ v0.6.2_75_g973361c0d.bin file and press the “Download” button (or go to siliconchip.au/link/abpo). In a few seconds, Micropython version 0.6.2 will be installed on the device. Next, select the facedetect.kpfg file and press the download button again. This will install the facedetect.kpfg model onto the device. The registered number 0x300000 can be changed by entering the changed value into the “flash-list.json” file of the facedetect. kfpkg model. Note that the later versions of Micropython are available, but their bigger file size means the classifier model might not load properly. To upload the entire project, you need to install the Maixpyide on your computer, which you can download from https://dl.sipeed.com/MAIX/ MaixPy/ide/ After installing it, connect the device by pressing the connect button at the bottom left of the window (the chain symbol). Go to the File Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the Silicon Chip Online Store. Email your circuit and descriptive text to editor<at> siliconchip.com.au menu and open the python program (“doorman_mod1.py”). Then press the play button at the bottom left of the window. To transfer the program to the Maixpyide so it runs every time the device is powered on, go to the Tools menu and select ‘transfer file to board’. This command will transfer the file to the Maixduino and rename it to “boot.py”. This will make the program run every time the device is powered on. There is a complete guide to the Maixpyide at siliconchip.au/link/abl0 AI-powered face detection is nothing new today. It can be done easily by a powerful computer. However, the fact that a standalone 5V-powered Maixduino microcontroller module can perform this task shows that AI is not limited to only powerful computers. It is spreading to microcontrollers now! Bera Somnath, North Karanpura, India. ($120) The Maixduino Sipeed M1. Source: https://w.wiki/6Uih Australia's electronics magazine October 2023  63 How to program SMD microcontrollers with TQFP Programming Adaptors Our new PIC Programming Adaptor, described last month, can program many chips in DIP, SOIC, MSOP, SSOP and TSSOP packages. But SMD micros come in other packages, including SOT-236 and QFPs (quad flat packs). This article explains how to program such devices out-of-circuit with several reconfigurable programming jigs. By Nicholas Vinen T hese jigs are inexpensive and straightforward to make. Still, they are invaluable if you need to program SOT-23-6 or QFP microcontrollers before being soldered to a board, such as when the board lacks a programming header. They aren’t limited to PICs; they will work with most microcontrollers in these packages, including AVRs and many ARMbased types. We use jigs like these all the time to program chips we sell, including the ones below: ● The 64-pin PIC32MX470F­ 512H-120/PT programmed for the Micromite Plus (Explore 64). ● The 100-pin PIC32MX470F­ 512L-120/PF, also for the Micromite Plus (Explore 100). ● The 44-pin PIC16F18877-E/PT for our recent Wideband Fuel Mixture Display (WFMD). ● The 32-pin ATSAML10E16A-AUT for the High-Current Battery Balancer. Those are all QFP chips but with different numbers of pins, so a separate jig is needed for each one. Note that sometimes QFP chips with the same number of pins can be different sizes, so you may need more than one jig with the same pin count. However, as our jigs are reconfigurable, you only need one of each, even if you need to program different chip types in that package. Most QFP micros actually come in either TQFP (“T” stands for “thin”) or LQFP (“low-profile”) packages. The sockets we’re specifying suit TQFP, although other types may be available. Let’s go through the jigs individually, from the fewest pins to the most. SOT-23-6 This suits tiny PICs like the PIC10(L) F202-I/OT or PIC10(L)F322-I/OT that we used in our Remote Control Range Extender (January 2022; siliconchip. au/Article/15182). These often need to be programmed out-of-circuit because they’re typically used on very small PCBs that probably don’t have much room for a programming header. This is the simplest jig as it is just made of a commercial SMD to DIP adaptor (AliExpress siliconchip.au/ link/abmu) plus five female-to-male jumper leads. It is shown in Photo 1, and the wiring is shown in Fig.1. Fig.1: here’s how to wire a PICkit 4 to an SOT-23 programming socket via jumper wires. It might not look ‘kosher’ but we’ve found it works fine, even without local supply bypassing for the PIC being programmed. Photo 1: the SOT-23-6 ‘test socket’ can be wired to a PICkit 4 using five male-female jumper leads. Then tape or glue them together where they go into the PICkit. This work fine despite the lack of bypass caps (the software verifies the programming so it would catch any errors). 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.2: our four TQFP programming adaptors all follow this basic configuration, designed for maximum flexibility. The headers around the socket make it easy to connect any pin to GND, Vcc, Vdd or one of the pins on the programming header (CON35/CON36) via jumper wires. The optional regulators at the top can derive two different Vdd & Vcc supply rails from an external DC source. siliconchip.com.au Australia's electronics magazine October 2023  65 While there are no bypass capacitors or anything like that, we’ve found it works fine as long as the jumper leads are kept short. If you come across a different micro in the same package that uses a different pinout, rearranging the jumper wires to suit will be simple. The socket is pretty expensive at about $55, including delivery, but it works well, and there aren’t many better options. If you only need to use it occasionally, a cheaper option is to design a PCB with an SOT-23-6 footprint wired to a programming header. Then, instead of soldering the chip to its footprint, simply hold it in place with a clothes peg or similar. That can work surprisingly well, but it’s fiddly. We would only do that for the occasional chip; we wouldn’t want to program dozens that way. TQFP-32, -44, -48 & -64 We have two options for TQFP package chips. The first is the simplest but only suits chips like the ATmega328P. They are so common that you can get an adaptor that converts the pinout to the through-hole (DIP-28) equivalent. For example, this one costs $19, including delivery, at the time of writing: siliconchip.au/link/abmv Fig.3: how the 32-pin TQFP programming adaptor rig would look if you fit all the components. That would give you all the options you need for programming any chip in this package, but in most cases, you can save yourself a bit of time and a few dollars by only adding the components you need for programming a given micro. Fig.4: this shows how we built a very minimal programmer for the ATSAML10E16AAUT ARM-based microcontroller from Atmel (now Microchip) on the same PCB shown in Fig.3. That chip is programmed using the AVR SWD (serial wire debugging) protocol, which uses different pins on the PICkit 4 8-pin header compared to PIC programming. Australia's electronics magazine Say you have a means of programming a DIP ATmega328P, such as a TL866II or the newer T48 (that we reviewed in the April issue). In that case, you just need to purchase the SMD adaptor, slot it into that programmer and away you go – see Photo 2. A more flexible option that also works with chips like the ARM-based ATSAML10E16A mentioned above is our custom adaptor board that accepts a commercial TQFP programming/test socket. Its circuit is shown in Fig.2 and the matching PCB overlay in Fig.3. There are relatively few components on it, so it’s pretty easy and inexpensive to build. Our larger 44-pin, 48-pin and 64-pin adaptors follow the same pattern, so the following description will cover all of those. PCBs for all four versions are available from the Silicon Chip Online Shop. The test sockets are well made, have gold-plated contacts for a long life and only cost about $15-25 each. We have links to each one we’ve tested in the parts list. They have a staggered pin pattern unsuitable for use with protoboard and such, hence our custom PCB designs. Each PCB suits a specific socket. Surrounding that socket, we have six rows of headers with one pin for each socket pin. The three closest to the socket allow you to use a jumper to connect that pin to GND or one of two power supply rails. You can also plug in a female header upside-down that lets you connect a capacitor from that pin to GND, or a capacitor to GND plus a connection to the supply rail. For pins used for programming, it’s a simple matter of fitting a short female-female jumper lead between the pin in the middle row and one of the ICSP header pins. Two sets of headers are provided to make it easy to connect these pins to an ICSP dongle like a PICkit or Snap programmer (PICkits can program AVRs now too). The second set of three headers allows you to choose, for those pins connected to a power rail, which power rail that is. That is done by placing a jumper between the centre pin and either the Vcc or Vdd row. Note that most micros don’t need two rails for programming, so you can use Vdd exclusively for those, but we wanted to provide maximum flexibility. Each set of Vcc and Vdd pins along each side of the chip has a pair of siliconchip.com.au ◀ Photo 2: this socket comes pre-mounted on a small PCB with a pair of SIL headers on the underside. They are routed to match up the pinout of the TQFP-32 version of the ATmega328 (and similar chips) to the DIP-28 version, so a standard DIP programer can be used to program the TQFP chips. bypass capacitors to GND. This means you can get away without needing to add bypass capacitors closer to the chip in most cases; you can simply use jumpers to connect GND and Vdd where required. Two adjustable or fixed linear regulators can be mounted in the board’s upper left and upper right corners to supply either the Vcc or Vdd rail. In most cases, we use a PICkit to deliver power to Vdd via its header and don’t bother with these. But again, this gives you flexibility. Using these regulators, you could derive Vcc and/ or Vdd from USB 5V, a plugpack or a bench supply. Pads are also provided to fit SMD LEDs to show when the Vcc and Vdd rails are powered. Finally, there are rows of pairs of uncommitted pins that you can use for jumpering signals if required. The only connections on the board are between the pairs of pins. Fig.4 shows the minimal parts needed to configure this board for programming the ATSAML10E16A, while Photo 3 shows our actual jig. That demonstrates that you only need to fit the parts you need for a particular application, and you can add more siliconchip.com.au later if necessary. Here, we’re using the PICkit 4 in its CORTEX SWD mode (it also supports AVR ISP, among other protocols). One thing to note about these jigs is that the space around the socket is tight. That’s because we’ve broken out the pins close to it, keeping the track lengths as short as possible. It’s a little squashed, but we’ve programmed ◀ Photo 3: a minimalist assembly of the 32-pin TQFP adaptor set up for the chip stated on the label. Labelling the adaptors so you can remember what chips they are set up for is a good idea. hundreds (if not thousands) of chips with these jigs and haven’t had any real difficulty getting them in or out. However, that could be a good reason to avoid fitting parts you don’t think you’ll need. There are mounting holes in the corners for tapped spacers, so the jig sits flat on a bench. That makes them much easier to work with. Fig.5: here’s where all the components go on the 44-pin TQFP programming adaptor. This package is pretty common for 8-bit PICs (eg, PIC16F18857 and PIC16F18877), 16-bit PICs (eg, dsPIC33FJ128GP804), 32-bit PICs (eg, PIC32MX170F256D-I/PT) and AVRs (eg, ATmega644PA). October 2023  67 Fig.6: this shows how we wired up our assembled 44-pin TQFP programming jig to suit PIC16F18877-I/ PT chips. Target power is delivered by the PICkit. The programming connections go via the pins on the “Pwr” row and then via jumpers to the IC pins to keep them away from the front socket opening. Fig.7: here’s where the components go for the 48-pin TQFP Programming Adaptor. We have the parts to build one but haven’t done so yet because micros in this package are far less common than either 44 pins or 64 pins. We have placed a large filled circle on the PCB silkscreen at the upper-left corner of each TQFP socket to indicate where pin 1 of the IC would typically go. You then line up the dot or divot on the chip with that marking. All that means is that the pin number labelling on the headers will be correct when the chip is orientated like that. You could use a different orientation and reroute the connections to suit if you wanted to, as there are no fixed connections to the socket on the board. Still, keeping pin 1 in the upper left-hand corner is less confusing. 68 Silicon Chip TQFP-44 programming rig We haven’t drawn the circuit for this one as it’s the same as Fig.2 but expanded for the extra pins. The PCB overlay is shown in Fig.5. Photo 4 shows our jig, currently configured for the PIC16F18877-I/PT, while Fig.6 shows that wiring. Other chips we’ve programmed with this rig include the PIC32MX170F256D-I/PT and ATmega644PA. Note in Photo 4 how we’ve plugged a 3-pin socket into the header for pin 28 (Vdd) with a capacitor soldered across one pair of pins and a short wire across Australia's electronics magazine Photo 5: the 64-pin TQFP Adaptor board set up for a PIC32MX470. If you don’t need to make connections to the pins on the top row of the socket, especially in the middle, it can pay to leave those headers off, as it might allow you to open the socket clamshell wider, making it easier to get chips in and out. the others. It acts as a jumper to connect Vdd to that pin while providing a bypass capacitor to GND. TQFP-48 programming rig Again, the circuit is the same as Fig.2 but with extra pins on the socket, while the PCB overlay is shown in Fig.7. We haven’t built one yet as we don’t need it. That’s because most microcontrollers in 48-pin TQFP packages are ARM-based types that we haven’t used (from Infineon, Renesas or Silicon Labs). Still, we designed the board and siliconchip.com.au Photo 4: here, we have installed all the headers around the 44-pin TQFP socket to make the Adaptor more flexible. Note the addition of a bypass cap on one of the supply pins using an upside-down three-pin socket. A closeup of the ‘jumper’ made out of a 3-pin socket and capacitor we had to make is shown below. Fig.8: this is the 64-pin version of the TQFP Programming Adaptor. It’s a reasonably common package, especially for 32-bit PIC microcontrollers and some PIC16s, PIC18s, PIC24s, dsPIC33s, Atmel ATSAM chips and more. This is basically the same as the other boards but with more socket and header pins. Fig.9: the 64-pin Programming Adaptor set up for the PIC32MX470F512H-120/ PT used in the Micromite Plus. We removed the plastic from some headers for pins 53-55 and 58-60 so they would sit lower and give more clearance for the TQFP socket hinges. They’re still long enough to fit jumpers. sourced a socket, so we decided to make the PCB available to anyone who might need it. TQFP-64 programming rig Again, this circuit is simply that of Fig.2 but with twice as many socket pins and associated header pins. The PCB overlay is shown in Fig.8, with Fig.9 being the minimal configuration for programming a PIC32MX470F512H-120/PT or similar (this should also suit 64-pin dsPICs). Photo 5 shows our jig for programming the PIC32MX470F512H-120/PT. siliconchip.com.au We also built a TQFP-64 programming jig for the powerful PIC32MZ2048EFH064-I/PT chip that Phil Prosser likes to use in his projects. As shown in Photo 6, we didn’t use our custom board for this but instead purchased a socket that came on a PCB with 16-pin headers on all four sides (on the underside). We then mounted that on a protoboard via four 16-pin sockets and soldered the bypass capacitors and programming header to that. Connecting the pins to GND, Vdd and the programmer pins was done by point-to-point Australia's electronics magazine wiring using Kynar (wire wrap wire), which is thin but stiff and easy to work with. We could have used the custom jig in this role, but we wanted to try a different approach. It was a little work to do this but it worked fine. At the time of writing, this adaptor costs $30, including delivery and can be purchased from siliconchip.au/link/ abmw TQFP-100 programming rig We haven’t bothered to make a custom 100-pin board for a few reasons. October 2023  69 Photo 6: as an alternative approach, this 64-pin TQFP socket was purchased already fitted to a board with headers on the underside. We then soldered matching sockets on a piece of protoboard and hardwired a programmer for the PIC32MZ. It’s a bit less flexible than the other approach, but it works. Photo 7: this hand-made 100-pin TQFP programming adaptor has served us well, programming all the PIC32MX470 chips for the Explore 100. The added protoboards (joined by two wires across the back, for Vdd & GND) can be unplugged as they are on sockets that fit the pre-existing headers. Parts List – TQFP Programming Adaptors Parts required for all versions 1 6- or 8-pin header, 2.54mm pitch 1 6- or 8-pin right-angle header, 2.54mm pitch 16 M2012/0805 100nF 50V X7R ceramic capacitors 10 small jumper shunts 3 short female-female jumper wires 4 M3 tapped spacers 8 M3 × 6mm panhead machine screws 4 M3 hex nuts 1 serial programmer to suit chip(s) being programmed TQFP-32 programming adaptor 1 double-sided PCB coded 24108231, 95 × 82.5mm 1 TQFP-32 ‘clamshell’ test/programming socket [siliconchip.au/link/abmy] 24 8-pin headers, 2.54mm pitch TQFP-44 programming adaptor 1 double-sided PCB coded 24108232, 95 × 82.5mm 1 TQFP-44 ‘clamshell’ test/programming socket [siliconchip.au/link/abmz] 24 11-pin headers, 2.54mm pitch TQFP-48 programming adaptor 1 double-sided PCB coded 24108233, 95 × 82.5mm 1 TQFP-48 clamshell test/programming socket [siliconchip.au/link/abn0] 24 12-pin headers, 2.54mm pitch TQFP-64 programming adaptor 1 double-sided PCB coded 24108234, 95 × 82.5mm 1 TQFP-64 test/programming socket [siliconchip.au/link/abn1] 24 16-pin headers, 2.54mm pitch Optional parts for all boards 1 or 2 M3216/1206 SMD LEDs plus 1kW M2012 resistors (for VDD/VCC indication) 1 two-pin female header plus M2012/0805 22μF 6.3V X5R capacitor (for micro pins that need a capacitor to GND) 1+ three-pin female header plus M2012/0805 100nF 50V X7R capacitor (for micro pins that need local bypassing) 1 2×8 pin DIL header, 2.54mm pitch (for extra GND terminals) 2 2×20pin DIL header, 2.54mm pitch (for extra connecting terminals) Extra parts per onboard regulator (up to two regulators per board) 1 LP2951D adjustable linear regulator, SOIC-8 (REG1/REG2) 1 50kW top-adjust multi-turn trimpot (VR1/VR2) 1 27kW 1% M3216/1206 or M2012/0805 SMD resistor 2 4.7μF 25V X5R M2012/0805 SMD ceramic capacitors 1 10nF 50V X7R M2012/0805 SMD ceramic capacitor 1 4-pin header, 2.54mm pitch 1 3-pin header, 2.54mm pitch 1 jumper shunt 70 Silicon Chip Australia's electronics magazine For a start, we have programmed only one 100-pin micro to date, the PIC32MX470F512L-120/PF used for the Micromite Plus Explore 100. So we only needed a simple fixed jig. We were able to buy a 100-pin socket pre-mounted on a PCB with two pairs of 50-pin DIL headers. It was relatively easy to solder strips of protoboard to these headers and then use that to add bypass capacitors, a programming header and the connections necessary for programming, as shown in Photo 7. It’s a little dusty, but it works! As with the PIC32MZ rig, the protoboard is attached via sockets, so we could theoretically unplug them and change the socket to work for a different micro if we need to. Note the two wires running across the back of the socket that join Vdd and GND between the two sides. The programming header is on the underside of the left-hand board and is just visible in the photo. The point-to-point wiring was done using Kynar wire-wrap wire, as it’s easy to work with. This adaptor costs $50, including delivery at the time of writing, and can be purchased from siliconchip. au/link/abmx Conclusion These programming rigs are somewhat specialised, but they certainly come in handy when you need them. You might build one when embarking on a project that uses a particular chip, and you could build up a collection over time as you work with micros in different packages. We put some effort into creating these PCBs to make them flexible and easy to work with. So any readers with similar needs would benefit from being able to use our PCBs and follow the same general strategies. SC siliconchip.com.au Subscribe before prices increase on November 1st SEPTEMBER 2023 ISSN 1030-2662 09 The VERY BEST DIY Projects ! 9 771030 266001 $1150* NZ $1290 INC GST Stylish Speakers made using IKEA Salad Bowls (page 18) 8- to 40-pin PIC Programming Adaptor (page 64) The most interesting products at Electronex and Australian Manufacturi ng Week Broadcast Radio the story of 100 years of radio in australia Australia’s top electronics magazine Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. 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To start your subscription go to siliconchip.com.au/Shop/Subscribe INC GST Mk2 0-30V 0-2A bench supply Part 2 by John Clarke This revised Bench Supply is basic yet feature-packed, with full onboard metering and an adjustable current limit. It’s pretty easy and cheap to build, so is suitable for relative beginners, and handy for various purposes, including powering circuits for testing or development. Let’s get to building it. P art of the reason for the 30V and 2A limits is that they allow us to use a modestly-­ sized transformer that fits neatly alongside the regulator board in a compact 160 × 180 × 70mm benchtop instrument case. The Supply is small enough to stay out of your way but powerful enough for many jobs. You could even stack two or three to have a few different voltages available or connect two in series to form a split supply. Just keep in mind that their current limits will be enforced separately, so if there is a fault, it’s possible that one Supply would go into current limiting while the other(s) wouldn’t. While this is a mains-based project, anyone who is good at following instructions and with reasonable soldering skills should be able to build it safely. Just make sure you perform all the wiring exactly as described using correctly rated wire, and don’t skip any of the required insulation or cable ties. 72 Silicon Chip Before we get to construction, a word about the metering. We tested some low-cost volt/ammeters from eBay but found that they were too inaccurate, which is why we specified the part from Core Electronics. Use caution if you want to substitute another meter, as its readings could be way off. If you missed the first part last month and are wondering why we’re revisiting this design after just one year, it’s because the multi-tapped transformer used in the 2022 version is no longer available. This version uses a readily-available transformer with independent 12V+12V secondaries, each tapped at 9V, wired in series. A small voltage inverter module makes up for the lack of a 30V tap. As with many projects, the first step in construction is soldering the majority of the components to the printed circuit boards. Construction Most of the parts for the Supply Australia's electronics magazine mount on three PCBs. The main 76 × 140mm PCB is coded 04107223 and includes most of the components, while a smaller 56 × 61mm PCB coded 04105222 has the front panel parts such as voltage and current setting potentiometers, indicator LEDs and load switch. A 14-way ribbon cable with insulation displacement connectors (IDCs) joins the two PCBs. The voltage inverter circuitry uses a 37 × 42.5mm PCB coded 04107222 that mounts vertically on the main board using short tinned copper wire links and a support wire at the top. As explained last month, there is the option to use a single 2.5kW multi-turn potentiometer for VR1 or a standard single-turn 5kW potentiometer in conjunction with a 5kW multi-turn trimpot (VR2). If you are using the 2.5kW multi-turn potentiometer, VR2 is not used and must be left off the PCB. During the following process, refer to the PCB overlay diagrams (Figs.3 & 4) to see which parts go where. siliconchip.com.au Begin construction with the main PCB (Fig.3) by fitting the two surface-­ mount components. These are the INA282 shunt monitor (IC2) and the 20mW resistor. For the resistor, we have made provision on the PCB for either two 10mW resistors in series or a single 20mW resistor. Both the resistor and IC are relatively easy to solder. Find the pin 1 orientation marker on the INA282. This can be a dot on the top face, a notch at the pin 1 end of the device, or a chamfer along the pin 1 to 4 edge of the package. Position the IC over the pads and solder a corner pin using a fine-tipped soldering iron. Once soldered, check the alignment against the remaining IC pin leads and PCB pads. Remelt the solder and realign the IC if necessary until each pin aligns with its pad, then solder the remaining pins to the PCB. Any solder bridges can be fixed using solder wick with flux paste to draw up the excess solder. The surface-mounting resistor can be soldered similarly, one end at a time. Straighten the resistor by remelting the solder and nudging it after the first end is soldered should it be skewed. The next components to be installed are the through-hole (axial) resistors. The resistors have colour bands, but it is a good idea to check the values using a multimeter too. Fit the 12 diodes of four types next. They are all polarised and must be orientated as shown in Fig.3 and the screen printing on the PCB. Use the smaller glass-encapsulated 1N4148 diodes for D5, D6 and D9. On the other hand, diodes D1, D4, D7, D8 and D10 are larger 1N4004 devices, while D2 is a larger still 1N5404 diode. The three remaining diodes are zener diodes ZD1, ZD2 and ZD3, which are in medium-size glass packages. ZD1 is 33V (1N4752) while ZD2 and ZD3 are 12V (1N4742) types. Ensure each is installed in the correct position and with the correct orientation. Operational amplifier (op amp) IC1 can now be installed, taking care to orientate it correctly. This can be mounted using a socket or directly on the PCB. Follow with transistors Q2-Q6 and REG2. These all are in TO-92 plastic packages, so be sure the correct device is installed in each location. Q2 is a siliconchip.com.au Fig.3: the components fit on the main PCB as shown here; watch the orientations of the polarised parts. VR2 is only needed if VR1 is 5kW; in that case, it has the adjustment screw towards the top like the other trimpots. Leave Q1, REG1 and the inverter module off until the case has been prepared. Ensure the sockets for CON1 and CON2 are orientated as per the photos, so that the wires entries are not blocked by other components. Fig.4: this board carries the front panel controls and indicator LEDs. Potentiometer VR3 is held to the board using PCB pins, and its terminals are also connected via PCB pins. VR1 is attached using brackets on either side of its body and connected to its three pads (labelled “Anti CW”, “Wiper” and “CW”) via short lengths of wire. Australia's electronics magazine October 2023  73 An internal photo of the completed Supply minus both PCBs, so you can more clearly see where the various other parts mount and how the wiring is run. Note the locations of the three plugs in the lower portion, ready to plug into the main PCB. 2N7000 while Q3-Q5 are BC547s and Q6 is a BC327. REG2 is the LM336-2.5. Mount the trimpots next. These are top-adjust multi-turn types; two are 10kW (VR6 and VR7), one or two are 5kW (VR2 and VR4), while VR5 is 100W. The 10kW trimpots might be labelled 103, the 5kW trimpots as 502 and the 100W trimpot as 101. Be sure to orientate these with the adjustment screws as shown in Fig.3. Note that if using a 2.5kW multi-turn pot for VR1, VR2 is not fitted. Now install rectifier bridge BR1; the diagonally cut corner is the positive side, so make sure that it is orientated as shown. You can install the three and fourway pluggable terminals for CON1 and CON2 now. Ensure these are orientated correctly by inserting the plugs into the sockets first, then rotating them so that CON1’s screw heads face toward CON3 and CON2’s screw heads are toward the edge of the PCB. Then solder the terminals in place, followed by box header CON3, with its notch facing as shown. There are 12 test points located around the PCB. You can fit PC stakes/ pins in each or leave them bare and use your multimeter probe directly 74 Silicon Chip onto the PCB pad instead. It is easier to have a PC stake at TP GND so that you can use an alligator or crocodile clip connection for measurements with respect to 0V. If fitting the PC pins, do that now. Mount the capacitors next. The 100nF, 10nF and 1μF ceramic types can be installed either way, but most of the electrolytic capacitors are polarised and must be inserted with the polarity shown. The positive side usually has a longer lead, while there Fig.5: this shows the components on the voltage inverter module. Ensure the electrolytic capacitors, IC1 and the diodes are all correctly placed and orientated. The electrolytic capacitors lie flat against the PCB. Australia's electronics magazine is a stripe on the negative side of the can. The 10µF capacitor marked NP is non-polarised and can insert either way around. Now fit relay RLY1 and two-way header CON7. Leave Q1, REG1 and the voltage inverter module off for now. Front panel PCB assembly The front panel PCB (Fig.4) has components mounted on both sides. The potentiometers, switch and LEDs are on the top, while CON4-CON6 are mounted on the underside. It is easier to solder in the 14-way box header (CON4) first so that you have full access to solder its pins on the top side of the PCB. It is installed on the underside of the PCB; ensure it is orientated correctly before soldering it in place. Next, install the six PC stakes for VR1 and the three for VR2. Then fit CON5 on the underside of the PCB, with its wire entries towards the nearest PCB edge. Mount switch S2 on the top side of the PCB. This sets the height position for the potentiometers and LEDs; however, LED1 and LED2 are mounted after the front panel holes are drilled and LED bezels are inserted. siliconchip.com.au Fit VR2 next, but first cut its shaft so that the length from the top of the threaded mounting boss to the end of the shaft is 15mm. VR2 is supported by PC stakes soldered to the potentiometer body. You need to scrape off the passivation coating in the area where the PC stakes will be soldered so that the solder will adhere. Solder it so that the top of the threaded section matches that of switch S2. Once it is in place, make the electrical connections to the potentiometer using PC stakes. Mounting VR1 The mounting method for VR1 depends on whether you are using a single-turn or multi-turn pot. The circular cut-out allows the multiturn potentiometer to pass through the hole. Solder right-angle brackets to the back of the PCB and use a cable tie to position the pot as shown above. Connect short wires from the pot terminals to the wiper, anti-clockwise and clockwise terminals on the PCB. Similarly, if using a single-­ turn pot, it is held in position by right-angle brackets soldered to the pot body and the PCB. The brackets need to be soldered to the PCB such that they reach the pot body and there is some overhang from the cut-out. Again, you will have to scrape off the passivation coating from the pot body where you will solder the brackets. For a single-turn pot, solder its terminals directly to the PC stake connection points. The main PCB (with voltage inverter attached) and both sides of the front panel PCB are shown at actual size. Compared to the original Bench Supply design, the main PCB uses a larger PCB which fits around the transformer. The front panel PCB is unchanged. Voltage inverter The -8V inverter module is assembled as shown in Fig.5 (also see the separate article starting on page 90 last month). We use a 220W 1W resistor for R1 and a 12V 1W zener diode (ZD1) to regulate the supply for the inverter to 12V. Make sure the electrolytic capacitors, IC1 and the diodes are all correctly placed and orientated. The finished PCB is installed vertically on the main PCB using short lengths of 0.7mm tinned copper wire or component lead off-cuts. Connect the Vin, GND and Vout on the inverter module to the main PCB at its matching Vin, GND and Vout pads. siliconchip.com.au Australia's electronics magazine October 2023  75 Making the ribbon cable Fig.6 shows how the IDC line sockets are attached to the ribbon cable. Ensure the 14-way wire and sockets are orientated correctly, with the notches positioned as shown, before compressing the connectors. You can do this by placing a small piece of soft timber (such as radiata pine) over each side of the connector and compressing it with a G clamp or bench vice. Alternatively, you can use a specialised IDC crimping tool. Metalwork Close-ups of the components and wiring behind the front panel. Note the mains switch insulation. Now it’s time to drill and shape holes in the baseplate of the enclosure and the heatsink, as shown in Fig.7. Rectangular and similarly-shaped cut-outs can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece and filing the job to a smooth straight finish. The power switch hole must be sized so that it stays clipped in when inserted into the cut-out, so take care when shaping it. The banana sockets have ovalshaped holes (“F”) that can be made by first drilling round holes and then using a round file to elongate them. There are four holes for mounting the regulator, power transistor and thermal switch on the rear panel; these are the holes marked “A” not near the mains input socket. After drilling them, clean them up around the edges on both sides with a deburring tool or a larger drill bit, so there are no sharp edges around the hole perimeters. This will avoid puncturing the insulation pads for the regulator and transistor and allow the heatsink to sit flat against the rear panel for maximum heat transfer. Fig.6: fit the IDC line sockets to the cable as shown here. This way, pin 1 is correct on both sockets but having them on opposite sides makes routing the cable easier once everything is in the case. Note that some sockets don’t come with the third locking bar over the top, in which case the ribbon cable isn’t looped. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.7: the shapes and sizes of some of the cut-outs are critical, so file them to shape carefully and periodically test to see if the parts fit in the holes. For example, the panel meter will fall out if its hole is too large, as will the rocker switch. For the binding posts (marked “F”), drill round holes, then elongate them to ovals using a round file. It would give even better heat transfer to the heatsink if you cut out a rectangular hole for the transistor, so the transistor and its insulating pad can be mounted directly against the heatsink instead of the rear panel of the case. However, we found that mounting onto the rear panel provided sufficient heat transfer to the heatsink, satisfactory for most uses of the Bench Supply. Still, if you require a high current at low voltages for an extended period, having this cut-out will reduce the transistor temperature. Once the drilling and cutting are finished, temporarily install the mains IEC input connector and then place the heatsink against the back panel with its side about 1mm away from the IEC connector and the top edge in line with siliconchip.com.au the top edge of the rear panel. Mark out the positions for the transistor, regulator and thermal switch holes on the heatsink through those already in the back panel. Make sure all the holes will be within the central mounting area of the heatsink and not through the fins, or the screws won’t fit. Once you’ve checked that, drill them in the heatsink, then deburr them for a smooth finish on the heatsink. regulator can later be attached to the rear panel via the pre-drilled holes using machine screws (temporarily secure the transistor and regulator to the rear panel with M3 screws and nuts). Adjust the leads so that the device tabs sit flat against the rear of the case. Then, ensuring the PCB is straight and not skewed in the case and the standoffs are directly on the base, solder the leads to the PCB on the top side. Case assembly Next, mark out the locations for the Attach the four 6.3mm-long M3-­ standoff mounting holes in the base tapped spacers to the corners of the of the case. Also mark out the mountmain PCB using 5mm M3 machine ing holes for the transformer. This sits screws. Next, insert the power transis- between the left edge of the PCB in-­ tor and the regulator leads into their between the PCB cutout and the left allocated holes in the PCB. edge of the case, leaving equal clearSlide the PCB so the transistor and ance on both sides. Australia's electronics magazine October 2023  77 Fig.8: the internal case layout and wiring. Take care that your unit is wired up exactly as shown here, especially the mains wiring, and don’t skimp on the cable ties, insulation or Earthing. 78 Silicon Chip After that, remove the transistor and regulator mounting screws. Solder the transistor and regulator leads on the underside of the PCB. Now drill the holes for the PCB and transformer (see Fig.8 for the component layout in the case). Also, drill the Earth lug holes in the base and scrape away the paint from around the holes so the Earth connections will be against the metal, not the paint. Attaching the heatsink The heatsink is a little taller than the enclosure. There are two ways of stopping the heatsink from touching the workbench, as the enclosure mounting feet are not tall enough to prevent this from happening. One option is to add extra spacers between the feet and the case, such as two M3 Nylon washers under each foot to raise the enclosure a little. This prevents the heatsink from touching the bench. Use the longer self-tapping screws supplied with the enclosure to secure the mounting feet. The second method is to cut the bottom of the heatsink off, so it is 67mm tall. That can be done with a hacksaw or a metal cutting saw. After you’ve sorted that out, apply a smear of heatsink compound to the rear of the heatsink. Press it onto the rear panel in its correct position and install the thermal cut-out using 15mm-long M3 machine screw and nuts. Leave the screws loose for the moment, so there is movement to adjust the mounting. Insert the 20mm screws for the transistor and regulator through the heatsink, then feed them through the rear panel. Place the TO-3P silicone washer for Q1 and TO-220 washer A close-up of the thermal switch wired up and insulated. for the regulator onto the screw ends. Now you can re-mount the PCB, with the mounting screws for the regulator and transistor passing through the device holes. Push the insulation bush into the regulator mounting hole before attaching it with a hex nut. For the transistor, add a steel washer against the device before attaching the nut. Secure the PCB to the base with M3 × 5mm screws and then tighten up the screws for the thermal cut-out, transistor and regulator, ensuring the heatsink stays square against the rear panel. The main PCB is attached to the base using four M3 × 5mm screws with Nylon washers. The washers allow the screws to tighten into the standoffs without touching the screws that enter from the top. Front panel label The panel label (see Fig.9) can be made using overhead projector film, printed as a mirror image so the ink/ toner will be between the enclosure and film when affixed. Use projector film that is suitable for your printer (either inkjet or laser) and affix it using clear neutral-cure silicone sealant. Roof and gutter silicone is suitable. Squeegee out the lumps and air bubbles before it cures. Once cured, cut out the holes through the film with a hobby or craft knife. For other options and more detail on making labels, see the page on our Fig.9: this front panel label can be downloaded as a PDF from the Silicon Chip website and printed out to form a label for the case. There is an alternative label without voltage markings to suit a multi-turn potentiometer. siliconchip.com.au Australia's electronics magazine October 2023  79 79 website: www.siliconchip.au/Help/ FrontPanels Insert the two LED bezels for the LEDs into the front panel and place the LEDs into the holes from the top side of the PCB, taking care to orientate them with the longer lead to the anode (“A”) side. Push the LEDs down onto the PCB but do not solder the leads yet. Break off the locating spigot on potentiometer VR3 (and single-turn potentiometer VR1, if used) and mount them onto the front panel with the washer on the pot side and nut on the outside. Then mount the on/off switch with one nut on first, to set the depth that the panel sits into the threaded section, then place the second nut on the outside to hold it in place. Move the LEDs off the PCB, insert them into the bezels and solder the LEDs in place. The front panel PCB is held in position by the switches and potentiometers; there is no need for extra support. If you wish, you can add 15mm-long standoffs at a couple of the corners. Now attach the pot knobs. For VR2, ensure the pointer is correctly positioned so it points to the end stops on the front panel label at both rotation extremes. Remaining parts Mount the IEC connector to the rear panel using M3 × 15mm screws and Summary of major test points TP1 is the negative voltage applied to REG1 via VR1 and VR2. It is measured with respect to GND (or V- at CON2) and can range from -1.2V to -1.3V. VR6 is adjusted to provide a 0V output at V+ on CON2 when VR1 is fully anti-clockwise. TP2 is the -2.49V reference. It is measured with respect to GND (or V- at CON2) and adjusted via VR7. TP3 is the current limit setting, measured between TP3 and TP10 at CON6, that ranges from 0V to 2V when correctly adjusted. The upper and lower thresholds are adjusted by VR4 and VR5, respectively. CON6 allows the current limit setting of VR2 to be measured using a multimeter or other floating voltmeter. TP4 is the negative supply and should read -8V to -9V relative to GND. TP5 is the output of current monitor IC2, giving 1V per amp of load current, measured with respect to TP2 (-2.490V). TP6 is the negative voltage applied to IC1a. TP1, the output of IC1a, should be within a few millivolts of TP6. See above for the significance of TP1. TP7 should be near 0V, rising toward 0.6V when power is switched off, measured with respect to GND. This is the AC detection voltage for the relay switching. 0V = AC detected, 0.6V = no AC detected. TP8 should rise from 0V to 13.6V with respect to GND over several seconds when power is first applied and drop quickly to near 0V when power is switched off. The time the voltage takes to rise from 0V to 13.6V is the switch-on delay. TP9 should be at about 12V with respect to GND, generated by zener diode ZD2. TP10 is the current setting offset to compensate current readings at TP5 (see TP3 above). TP21V is the positive supply and should measure around 21V with respect to GND. 80 Silicon Chip Australia's electronics magazine nuts, and the transformer to the base using four M4 × 10mm screws, star washers and nuts. The panel meter can be installed next. This is intended to slide and clip into the panel cut-out, but the top and bottom clips will not compress because they impinge on the seven-segment displays. The solution is to lever out the side clips to allow the internal PCB and displays to come out of the surround, then insert the surround through the front panel. The top and bottom clips can now be compressed so the meter can sit in the front panel. Once it’s in place, reinstall the meter internals. Mains wiring All mains wiring must be done using mains-rated cable. Be sure that brown wire is used for Active and blue wire is used for Neutral. The green/yellow-­ striped wire is for the Earth wiring only (see the wiring diagram, Fig.8). Connect the mains leads to the IEC connector and use a cable tie to secure the wires together and insulate using the rubber boot after it is cut so that the main section is 30mm long. This is so there is room for the transformer. Pass the wires through the boot before fitting it. The Earth wire from the IEC connector must go straight to the Earth mounting point on the case. This is attached using a crimp eyelet secured to the base with a 10mm M4 screw, star washer and two M4 nuts. If you haven’t already done so, scrape the paint away from around the hole to ensure the Earth connects to the metal of the case and not just the paint. The wires connect to the mains switch using female spade crimp connectors. Be sure to cable tie the wires together to prevent any broken wires from coming adrift. Additionally, cover the rear of the switch and the spade connections with 25mm diameter heatshrink tubing. Connect the transformer secondaries to CON1 using 7.5A-rated wire. Next, connect the IDC cable between the two boards and wire up the meter. The supply ground (thin black wire) for the meter is not connected and can be either cut short or connected to the NC terminal at the centre of CON5. That centre terminal is used as a wire keeper; it makes no electrical connection. Attach the banana sockets to the siliconchip.com.au front panel, wire them up to CON2 (black for negative, red for positive) and connect the Earth terminal to the chassis. Testing and calibration Before applying power, check your wiring carefully and ensure all mains connections are correct. If you are using a socket for IC1, insert it now with the proper orientation. Take care that none of its leads fold under its body during insertion. Wind VR1 fully anti-clockwise and VR3 a little clockwise from fully anti-clockwise. This sets the Supply to its minimum output voltage at a low current. Wind VR6 fully clockwise by turning it until a faint click is heard, or if you don’t hear a click, wind for 20 turns in the clockwise direction. This prevents the regulator output voltage from going negative initially before being set up correctly. Switch power on, and the voltmeter should show around 1.2-1.3V. Check that you can increase the output voltage by rotating VR1 clockwise. Do not go above 35V as the output capacitor is only rated to handle 35V. If the Supply does not appear to be working at this stage, recheck your construction. In particular, check that there is about -8V (or similar) at TP4 and about 21V at TP21V. Check that TP1 is around 0V. Re-check the component placement and soldering. Once the voltages appear correct, it is time to make adjustments. Firstly, the precision reference needs to be set. Measure the voltage between TP GND (or the negative output terminal on the front panel) and TP2, and adjust VR7 for a reading of -2.490V. Once adjusted, the regulator can be set to produce a minimum of 0V. This is done by initially winding VR1 fully anti-clockwise and measuring between the Supply’s output terminals. Adjust VR6 anti-clockwise until the reading just reaches 0V. Next, we set the maximum 30V output range. This is only if you are using a single-turn potentiometer for VR1. For the multi-turn potentiometer, ignore this step since VR2 is not fitted. For the multi-turn pot, the maximum voltage will be close to 30V when VR1 is wound fully clockwise, possibly a little more. Carefully adjust VR1 clockwise and stop where the voltage is 30V or when the pot is fully clockwise, whichever comes first. If the pot has reached full clockwise rotation and the voltage is less than 30V, adjust VR2 clockwise until you get a 30V output. If 30V is reached before full rotation, adjust VR2 anti-clockwise and VR1 clockwise a little each time until 30V is reached with VR1 fully clockwise. The current limit range is adjusted by rotating VR3 fully clockwise and measuring between TP2 and TP3. Adjust VR4 to obtain 2V. That sets the maximum current to 2A. The minimum current setting alters the lower end of VR3 to cancel out the offset voltage of IC2. To set this, rotate VR3 fully anti-clockwise, then measure between TP5 and TP10 and adjust VR5 for 0V. It shouldn’t be necessary to readjust VR4 again for the maximum current limit as the voltage adjustment made with VR5 will only change the maximum current setting by about 20mV, which is insignificant compared to the original setting at 2A. But you could SC tweak it again if you want to. The Supply should look like this once you have finished fitting all the parts and wiring them up. After checking it works, all that remains is to attach the lid using two of the supplied screws on either side. siliconchip.com.au Australia's electronics magazine October 2023  81 Using Electronic Modules with Jim Rowe 1.3-inch (33mm) Monochrome OLED Display Small monochrome OLED display modules have become widely available at a low cost in the last few years. Typically these measure only about 35×33mm but offer a 128×64 pixel resolution in a few different colours, like white or blue. Their I2C serial interface means that popular microcontrollers can easily drive them. O LED (organic light-emitting diodes) are solid-state light-­ emitting devices like standard LEDs. But instead of using a regular semiconductor P-N junction to emit light when passing a current, an OLED uses a thin film of an organic compound. As a result, displays using OLEDs tend to be thinner, lighter and use significantly less energy than those using traditional LEDs. In the last 15 or so years, they have become widely used in smartphones, handheld gaming consoles and, more recently, colour TVs. Small monochrome OLED displays are also used extensively in portable electronic equipment, so they have dropped significantly in price. Among the most popular are the 1.3inch (33mm) modules, such as the one shown in the photos. We have already used these in a couple of projects, like the MultiStage Buck/Boost Charger Adaptor from October 2022 (siliconchip.au/ Article/15510). These are available from a wide range of online suppliers, including via eBay, AliExpress and Amazon, and local suppliers like Jaycar and Core Electronics. Prices vary over a pretty wide range, about $5 up to nearly $20 from overseas suppliers, or around $15 from local suppliers (plus postage, if you’re getting them delivered). We also sell them in our Online Shop for $15 + P&P ($13.50 + P&P for subscribers), with catalog codes of SC5026 (blue) and SC6511 (white). These are not the smallest OLED modules available. Another common size is 0.96in or 24.4mm diagonal, with prices slightly lower than those for the 1.3in/33mm modules. These Fig.1: the block diagram of the SH1106 and SSD1306 controllers that are typically used in both the 0.96in and 1.3in OLED modules. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au generally have the same display resolution; the smaller size means those pixels are smaller. We used these in a few recent projects, like the Advanced Test Tweezers (February & March 2023; siliconchip.au/Series/396). There are also even smaller OLED modules, like those with a designated size of 0.49in/12.45mm. Those have a lower display resolution of 64×32 pixels. We used those in the original SMD Test Tweezers from the October 2021 issue (siliconchip.au/Article/15057). Inside the OLED modules The 1.3in OLED modules all use a single interface/controller and OLED driver IC, usually the SH1106 from Sino Wealth or the SSD1306 from Solomon Systech. The same controllers are used in the 0.96in modules. Fig.1 is a block diagram of the SH1106 and SSD1306 controllers. At upper left is the microcontroller (MCU) interface, which can be configured to interface with an MCU via an 8-bit 6800/8080-series parallel interface, a 3/4 wire SPI interface or an I2C serial interface. Most 1.3in and 0.96in OLED modules use the last option, I2C. Received display data is stored in the graphic display data RAM (the large block to the right of the interface), while commands are sent to the command decoder block at lower left. The display controller block at upper right uses the display data to drive the columns and segments of the OLED via the common and segment drivers shown at far right. The OLED has 64 common/column lines and 128 segment lines, matching the 128×64 pixel resolution. There are commands to update the display, turn the OLED display on or off, set the OLED addressing mode, set the column starting address, and adjust the OLED’s display contrast/ brightness (which also determines its operating current). The SH1106 and SSD1306 devices both come in very thin (0.3mm) SMD packages with over 260 contact pads. In the modules, they are mounted on the rear of the OLED screen itself. The module circuit Fig.2 is the circuit of a typical 1.3in monochrome OLED module based on the SH1106 device (those using the SSD1306 are very similar). The OLED is at upper right, with the SH1106 interface/display RAM/controller/ driver IC1 in the centre. The rest of the circuit (to the left of IC1) provides the module’s power supply and I2C input interface. Four-pin SIL header CON1 is used for both power input and the I2C interface. REG1 takes the incoming Vcc (typically around 5V) and steps it down to +3.3V to run both IC1 and the OLED. The +3.3V line also drives IC1’s reset circuit (it needs to be reset as soon as power is applied) and feeds the 4.7kW pullup resistors for the I2C interface lines, SCL and SDA. The SH1106 and the SSD1306 controllers can adopt an I2C address of either 0x78 or 0x7A, depending on the voltage applied to the DC input at pin 15. If the pin is pulled to ground (in this case, via a 4.7kW resistor), the controller adopts the 0x78 address, while if the pin is pulled up to +3.3V, it responds to the 0x7A address. That lets you run two similar OLED modules on the same I2C interface. Most of the modules are set for the 0x78 address when you get them, but Fig.2: the circuit diagram of the 1.3in OLED module with a SH1106 controller. The circuitry separate to the OLED matrix and controller is for providing power and the I2C interface. siliconchip.com.au Australia's electronics magazine October 2023  83 The rear of the 1.3in OLED module shown at twice actual size. it is relatively easy to swap the 4.7kW resistor over to the ‘pullup’ position to change the address to 0x7A if needed. Some 1.3in OLED modules have a 7-pin interface header instead of the 4-pin header shown in Fig.2. These modules allow the use of the faster SPI interface instead of the I2C interface we’re focusing on here. Now let’s focus on what is involved in driving one of these modules from an MCU like an Arduino Uno or Micromite. Connecting it to an Arduino Connecting a 1.3in OLED module to an Arduino Uno is relatively straightforward, as you can see from Fig.3. The GND and Vcc pins connect to the GND and 3.3V pins on the Arduino, while the SCL and SDA pins connect to the Arduino’s A5 (SCL) and A4 (SDA) pins, respectively. If using an Arduino Mega 2560, the arrangement is similar, but the module’s SCL pin goes to pin 21 of the 2560 and the SDA pin to the 2560’s pin 20. As for software support, if you go to the Arduino website and look at the library listings for “Display” applications (siliconchip.au/link/abl7), you will find quite a few libraries to do this job: Adafruit SSD1306, GyverOLED, OLED SSD1306-SH1106, OLED Display VGY12864L-03, ss_oled, ssd1306, ssd1306xled and U8g2. Another site (www.lcdwiki.com) offers a library called “1.3inch_IIC_ OLED_Module_SKU:MC130VX”, together with some documentation and three example sketches. All of these depend on the library U8g2, which you can download as a zip file from https://github.com/olikraus/ The three example sketches demonstrate how to draw graphics, text strings and a BMP image on the OLED, so they’re pretty informative. Screens 1 to 5 show some of the displays I was able to produce using these sketches and a blue 1.3in OLED module. Connecting it to a Micromite Connecting one of the 1.3in OLED modules to a Micromite MCU is also quite easy. Fig.4 shows the connections needed for driving the OLED module from a Micromite Plus Explore 64 (August 2016; siliconchip. au/Article/10040). Connecting the module to a Micromite Mk2 or LCD Backpack V1/V2/ V3 would be almost the same, except the module’s SCL pin would be connected to pin 17 of the Micromite and the SDA pin to pin 18. As with an Arduino, you need to install some software to let the Micromite drive the OLED module. That isn’t quite as easy as with the Arduinos, as there is no widely available Micromite OLED driver software yet. Still, because I knew that some Silicon Chip readers would want to drive an OLED module from a Micromite, I decided to try writing an MMBasic program to go through the necessary steps. Luckily, fellow Silicon Chip staff member Tim Blythman was able to offer some help, as he has done quite a bit of work with the smaller 0.96in OLED modules (which use the same SH1106 and SSD1306 chips) and is very familiar with the steps needed to drive them. Thanks to Tim’s help, despite losing some of my rapidly thinning grey hair, I was able to develop an MMBasic program that can drive one of these OLED modules from a Micromite. It demonstrates how text and simple graphics can be displayed on its screen. The ◀ Fig.3 (left): you can use this diagram to help connect a 1.3in OLED module to an Arduino Uno or similar. Fig.4 (below): how to drive the OLED module via a Micromite Plus Explore 64. You can similarly connect it to a Micromite BackPack by connecting SCL to pin 17 and SDA to pin 18. 84 Silicon Chip Australia's electronics magazine siliconchip.com.au Screens 1-6 (left-to-right, top-to-bottom): example output produced by the various test programs we downloaded or created for use with the 1.3in (33mm) OLED module. Screen 6 at lower right is from our Micromite program. program is called “OLED MODULE TEST Prog2.bas”, and the display it achieves is shown in Screen 6. It’s a pretty basic little program (no pun intended), and as it stands, it only demonstrates how the OLED module can display text and simple graphical symbols. It doesn’t let you type text in via the Micromite console and display it directly on the OLED; that would involve additional programming. That’s because the easiest way to drive these OLEDs is by setting the driver chip to Page Addressing Mode, which effectively divides the OLED screen into eight horizontal ‘pages’, each page consisting of 128 vertical segments eight pixels high. The pages are arranged vertically, with page 0 along the top of the screen, page 1 immediately below it and then the remaining pages descending until page 7 runs along the bottom of the screen, as shown on the left side of Fig.5. When the driver chip updates each page on the OLED (which it does one page at a time), it starts at the far left and displays the eight-pixel segments one after the other, moving from left to right. Each eight-pixel segment is sent in b0 to b7 order (‘LSB-first’), as shown on the right-hand side of Fig.5. This Page Addressing Mode makes it not too difficult to display lines of text; all you need to do is work out the sequence of segment bytes required to show the character or symbol you want to display, then send that sequence to the OLED controller as a sequence of single bytes. For text, it’s easiest to have a line spacing of 8 pixels, meaning the characters are around 7 pixels tall and perhaps 4-5 pixels wide. To help you do this, I have worked out the byte sequences for the upper case and lower case text characters, plus the basic numerals (0 to 9) and a reasonable number of common symbols. These are listed in a second dummy MMBasic program called “OLED MODULE textchar strings. bas”, which you can download from the Silicon Chip website along with “OLED MODULE TEST Prog2.bas”. That should allow you to write a program that can display up to eight lines of text on the screen of one of these 1.3in OLED modules. Drawing detailed graphics on the OLED screen is a bit more involved but, as the demonstration program shows how to write pixels into the OLED’s display RAM, that should provide a starting point for more advanced graphics. A reader with more programming experience might accept the challenge of creating a full display driver for these OLEDs, possibly based on the SC starting point I have provided. Fig.5: Page Addressing Mode divides the OLED into eight sections as shown. This is the easiest way to drive the OLED. siliconchip.com.au Australia's electronics magazine October 2023  85 Multi-function Weather Stations GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. FROM 7995 $ • Indoor & outdoor temperature • Temperature alert alarm • 12 Hour weather forecast XC0366 $79.95 A GREAT PRICE FOR A 7 MODELS PRINTER / ENGRAVER / GREAT VALUE! 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Jaycar reserves the right to change prices if and when required. Explore our full range of weather stations, in stock at over 110 stores, or 130 resellers or on our website. jaycar.com.au/weather-stations 1800 022 888 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 10/23 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) Basic RF Signal Generator (Jun23) ATmega328P-AUR RGB Stackable LED Christmas Star (Nov20) ATtiny45-20PU 2m VHF CW/FM Test Generator (Oct23) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) PIC12F617-I/P Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22), Active Mains Soft Starter (Feb23) Model Railway Uncoupler (Jul23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) GPS Disciplined Oscillator (May23) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Digital Boost Regulator (Dec22) PIC16LF15323-I/SL Remote Mains Switch Transmitter (Jul22) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC VARIOUS MODULES & PARTS - 5V 3-pin boost regulator module (2m CW/FM Test Generator, Oct23; SC6780) - 5V 3-pin buck regulator module (2m CW/FM Test Generator, Oct23; SC6781) - 20x4 blue backlit LCD with I2C interface (ESR Meter, Aug23; SC4203) - red & black PCB-mount banana sockets (ESR Meter, Aug23; SC4983) - two 1nF ±1% capacitors (ESR Meter, Aug23; SC4273) - 0.96in SSD1306-based yellow/blue OLED (RF Signal Gen, Jun23; SC6421) - CH340G-based USB/serial module (GPSDO, May23; SC6736) - NEO-7M GPS module with SMA connector (GPSDO, May23; SC6737) - GPS antenna with 3m cable and SMA connector (GPSDO, May23; SC6738) - DD4012SA 12V to 7.5V buck-converter module (GPSDO, May23; SC6339) PIC PROGRAMMING ADAPTOR KIT (CAT SC6774) (SEP 23) CALIBRATED MEASUREMENT MICROPHONE (AUG 23) Includes all parts, except the optional USB supply (see page 71, Sept23) $3.00 $4.00 $15.00 $6.00/set $2.50 $10.00 $15.00 $20.00 $10.00 $5.00 $55.00 SMD version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6755) $22.50 Through-hole version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6756) $25.00 Calibrated ECM set: includes the mic capsule and compensation components; see pages 71 & 73, August 2023 issue, for the ECM options (Cat SC6760-5) $12.50 DYNAMIC RFID/NFC TAG (JUL 23) Smaller (purple PCB) kit: includes PCB, tag IC and passive parts (Cat SC6747) Larger (black PCB) kit: includes PCB, tag IC and passive parts (Cat SC6748) $5.00 $7.50 siliconchip.com.au/Shop/ TEST BENCH SWISS ARMY KNIFE (APR 23) WIDEBAND FUEL MIXTURE DISPLAY (CAT SC6721) (APR 23) DIGITAL VOLUME CONTROL POTENTIOMETER (MAR 23) Short-form kit: includes PCB, all onboard SMDs, boost module, SIP reed relay & UB1 lid. Does not include ESP32 module, case, 10A relay or connectors (Cat SC6589) $50.00 - ESP32 DevKitC module with WiFi and Bluetooth (Cat SC4447) $10.00 - 3mm black laser-cut UB1 Jiffy box lid (Cat SC6337) $10.00 Short-form kit: includes the PCB and all onboard parts. Does not include the case, O2 sensor, wiring, connectors etc (see page 47, April 2023) $120.00 SMD version kit: includes all relevant parts except the universal remote control and activity LED (Cat SC6623) Through-hole version kit: includes all relevant parts (with SMD PGA2311) except the universal remote control and activity LED (Cat SC6624) ACTIVE MAINS SOFT STARTER (FEB 23) Q METER SHORT-FORM KIT (CAT SC6585) (JAN 23) RASPBERRY PI PICO W BACKPACK (JAN 23) Includes the PCB, all required onboard parts (excluding optional debug interface) and the front panel. Just add a signal source, case, power supply and wiring $100.00 RECIPROCAL FREQUENCY COUNTER KIT (CAT SC6633) Includes all parts, except the case, TCXO and AA cells (see page 57, July 2023) $60.00 (JUL 23) BASIC RF SIGNAL GENERATOR (JUN 23) DUAL-CHANNEL BREADBOARD PSU SONGBIRD KIT (CAT SC6633) (MAY 23) DUAL RF AMPLIFIER KIT (CAT SC6592) (MAY 23) SILICON CHIRP CRICKET (CAT SC6620) (APR 23) Includes all parts required, except the base/stand (see page 86, May 2023) Includes the PCB and all onboard parts (see page 34, May 2023) Complete kit: includes all parts required, except the coin cell & ICSP header $100.00 $30.00 $25.00 $25.00 $70.00 Hard-to-get parts: includes the PCB, transformer, relay, thermistor, programmed micro and all other semiconductors (Cat SC6575; see page 41, Feb23) $100.00 Complete kit: includes all parts in the parts list, except the DS3231 real-time clock IC (Cat SC6625; see page 56, January 2023) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - DS3231MZ real-time clock SOIC-8 IC (Cat SC5779) Kit: includes everything but the case, battery and optional pot (Cat SC6656) $60.00 $85.00 $7.50 $10.00 (DEC 22) Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, December 2022) Display Adaptor kit: complete kit (Cat SC6572; see page 45, December 2022) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK $40.00 $50.00 (SEP & NOV 22) GPS-version kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see September 2022 p63) $55.00 WiFi-version kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see November 2022 p76) $55.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE DATE NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 PCB CODE 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 Price $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER DATE JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 PCB CODE 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 01108231 01108232 04106181 04106182 15110231 01109231 24105231 04105223 04105222 04107222 Price $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $2.50 $2.50 $5.00 $7.50 $12.50 $10.00 $5.00 $10.00 $2.50 $2.50 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 OCT23 OCT23 OCT23 OCT23 OCT23 06107231 24108231 24108232 24108233 24108234 $5.00 $5.00 $5.00 $5.00 $5.00 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 SERVICEMAN’S LOG Watch out – delicate repair in progress Dave Thompson It’s tempting for a serviceman to jump into anything that needs repairing, especially if we feel confident about ourselves. It’s one thing to repair the dishwasher or install a new cistern in the bathroom, but a different kettle of fish to rewire a switchboard or install a new gas line! I’ve previously mentioned that while sitting in my workshop a few years ago, I felt the ground shake with an accompanying “BOOM!” sound. Those of you who know where I live will realise that I’m used to the ground shaking – as of today, we’ve had around 24,000 quakes since September 2010, so we’re all pretty good at gauging how strong an earthquake might be from the sensation now. Generally, anything over magnitude five will cause mild concern, but anything under that is just annoying. Anything over six and I worry the house will fall down, but it has survived a 6.4 and a 7.1 so far. It’s only the ‘big one’ we’ve been expecting for the last 50 years that worries me. This shake, however, was different. It was very short and sharp, and the boom was unusual. Many quakes ‘roar’ but they don’t typically make a sound like this one. It turned out that a house about five kilometres away had literally exploded, which is what I’d heard and felt. There was a lot of speculation about what had happened at the time. It transpired that some maintenance had been done on the reticulated gas system (in one of the few suburbs in this city with built-in gas), and a leak had caused 90 Silicon Chip a gas buildup overnight. When someone lit a flame in the house, kaboom! It really made a mess, and of the neighbours’ houses too. Fortunately, nobody was seriously hurt. Another home that went boom! In a similar incident, a leak caused a gas explosion in my wife’s sister’s home in Croatia. They use bottled gas, and a line to the cooker had somehow worked loose. When she went to light the cooktop, it blew their doors off and the windows out. It left her hearing impaired but otherwise OK; the same couldn’t be said for their apartment. The place was rebuilt by the time we stayed there, and they now use an electric stove. Both these stories are cautionary tales about getting people who know what they are doing to carry out maintenance and repairs on systems within our homes. This principle can be applied to anything. The home mechanic working on the brakes on their car, the avid DIYer installing their own solar panels. Under normal circumstances, that is all fine because those things are relatively straightforward. The brakes will likely work correctly, the solar panels will soak the sun and all will be well. However, in some cases, such as those outlined above, it pays to get the professionals in to do the job. It’s an important skill to know when you’re in over your head and you need to call the experts! It’s better to have your car towed to a mechanic to fix your mess than to realise you forgot to reconnect the brake line when the pedal goes to the floor... Over the years, I have come to accept this. While it hasn’t always been an easy decision to make – in many cases, I tried to accomplish something before realising it was time to call in an expert – there are still some things I will try to do myself. In doing so, I hope I’m not making things tougher for the person who comes after me to pick up the pieces, but of course, that isn’t always the case. I’m all for suggesting people give things a go, but the problem is that doing so can hurt our chances of success on the other end. A classic example of this is data recovery. Many attempt to follow walkthroughs on the internet, only to make things worse. When they finally bring their computer to me to ‘fix’, they’ve damaged their data by their attempts. With that in mind, I’m very careful when doing anything a bit ‘out of my wheelhouse’ so as not to cause further problems. Australia's electronics magazine siliconchip.com.au Items Covered This Month • • The delicate act of repairing yourself Fixing the vacuum pump in an electron microscope • ATA automatic gate repair • Reviving an electric motor Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com The pitfalls of wearing a watch Recently, my watch started playing up. I’ve worn a watch all my life and have gone through a fair few over the years. I’m not particularly hard on them, but as an engineer, there are times when they take a beating. I also had many jobs where wearing a watch was not allowed. For example, when working in the battery section of the airline, it was strictly forbidden to have anything remotely metallic anywhere near the batteries. Back then, there were two different types of batteries: lead-acid and NiCad. They do not play nicely together, so there were two completely separate (but adjacent) rooms for maintaining them without cross-contamination. The NiCad batteries especially were quite dangerous because each 24V battery comprised 20 individual high-­ capacity cells. These cells are connected by heavy metal links in a set order, and once the battery cover is removed, this presents a very real danger should anything metal drop into them. The wall of shame in the battery shop boasted several blobbed shifters (“crescents” here) and half-screwdrivers that someone had let loose onto a battery. As these batteries are capable of delivering a huge amount of instant current, anything metallic going into them was spectacular! Getting a watch or band across any of the links could mean losing a hand, so jewellery was forbidden. The old salt who ran the place would slyly ask for the time, and if I’d forgotten to take my watch off, I’d be dressed down a peg or two! The problem with taking a watch on and off all the time is that it wears everything out. The pins, the clasp and the strap all fail eventually from wear and tear. I went through many watches for this reason, and probably also because I was banging them against airframes and workbenches. I eventually bit the bullet and decided to buy a proper watch, a Tag Heuer Professional. It wasn’t cheap, but it was rugged, water resistant to way deeper than I’d ever swim. It also had a 1mm-thick sapphire crystal on it, which means it should be impervious to scratches and abrasion, something all the cheaper watches had succumbed to as I scraped and smacked them during my career. Long story short, I still wear this watch today after 30+ years. It looks as good as the day I bought it and has used a total of six batteries. I had it serviced every time the battery has been replaced. Usually, I’d take it to the place I purchased it from – which has since had to move location siliconchip.com.au because their original store was trashed in the quakes – and the same guy would look after it, as he has done for the last 25 years. This time, when I went into their new store, I learned that my guy had retired, and his son had taken over the business. I was assured everything would be the same: the same fine service, the same warranty and the same level of craftsmanship, yadda yadda... I was quoted a price for the service that was in line with what I’d paid over the years, allowing for the usual price increases. However, when I went to pick it up, the cost had ballooned. When I queried this, I was told that the bezel spring had worn out and needed replacing (this is a ‘dive’ type watch with a ratcheting bezel holding the crystal on). This cost an extra 80 bucks, and if memory served, had also been done before on a previous service. Fair enough; I trusted them to do what was best. They also replaced all the seals and O-rings, and pressure tested the watch (how? I don’t know) to ensure it really was sealed. This was important because if I go surfing or swimming, I don’t take my watch off, and I like to know it isn’t going to fill up with water. No time for my watch to die I got it home, and two weeks later, I woke up to it showing the incorrect time. I usually set it to an atomic clock app I have, and it is always within a second or two after three months, so I know it is an accurate timepiece. That morning, it was reading some two-and-a-half hours slow. This was the first time in 30 years that the watch had been wrong. I also noticed that the third hand, ticking away the seconds, no longer lined up with the markings on the watch face. When I first got this watch, I marvelled at how amazingly precisely the hand hit each second marker perfectly. I concluded that the people who’d serviced it, and who’d had the crystal off, had altered something, by accident or otherwise, and now I was seeing the results. Australia's electronics magazine October 2023  91 they were and what a useless klutz I must be – the usual factory-­floor hazing. The other guys there smirked knowingly because they’d been through it, too. My next exercise was to use a microscope and tweezers to re-bend this coil spring into a usable shape, or the airline would go broke because of my ineptitude! I spent the next hour sweating and getting the spring back into a proper shape, which is evidently impossible for anybody with brains. To my credit, I almost got there, and earned the foreman’s grudging respect. Later, he told me that most apprentices gave up after 10 minutes, but I’m stubborn like that! With that in mind, I had no doubt I could have this watch whipped into shape ‘tout suite’. Watch this... I reset the time and resolved to keep an eye on it over the next few weeks to see what would happen. The time didn’t change again, and it seemed accurate, but the third hand not hitting the marks really bothered me, so I did what anyone else would do and went back to the service agent. They looked at it, hummed and hahhed about it, and grudgingly agreed to check it out. I left it with them for another few days, after which they called to say it was ready. When I picked it up, they said they’d found nothing wrong with it and that the third hand issue was likely ‘wear and tear’ on the watch, as it was getting on a bit. I commented that it had been fine when I first took it there, but now it wasn’t. Again, the ‘old watch’ excuse was trotted out. I doubted they had done anything or even had it apart. I took it anyway and went on my merry way. A few months after all this, I was getting more annoyed with the hand not lining up. I don’t think I suffer from OCD, yet this was really bothering me. Timekeeping seemed fine, but I thought, how hard can it be to open this up and have a look? (Famous last words...) Fortunately, when I was going through my ‘buy everything I see from AliExpress’ phase, I bought one of those small watch vices and a kit of various watchmaker’s tools. No, I don’t know why either, other than to have them. So, I broke them out, blew the dust off them and set about seeing what I could do with this watch. Back in my apprenticeship days, I spent six months in the instruments workshop at the airline. This was in the days before avionics cockpit panels were ‘glass’, so plenty of analog instruments needed repairing, maintenance or calibration. As a rite of passage, on my first day there, I was given a gauge to ‘repair’ that I had to remove the bezel from. It was almost impossible to remove without distorting a coil spring sitting right behind it. This is, of course, a consumable part and must be replaced anyway. Still, as a n00b, I had no idea. And when I bent it, the foreman made a song and dance about how expensive 92 Silicon Chip Still, I had to be careful! Having skills 40 years ago doesn’t necessarily mean I have skills now. I used the tools I had to remove the back, then searched the web for how to remove the bezel, which required a bit of salt and pepper to pop the spring and detent. I’m always wary of just ripping into things like this, but that’s what it took in this case. As it turned out, I didn’t need to take the back off, but it did give me a chance to work with the watchmaker’s tools I’d bought, and they worked fine. With the bezel and crystal off, I could now gain access to the watch hands. The main hands were obviously OK because they worked, but that third hand still irked me. I asked myself: why would they take that off, anyway? Did they knock or bump it by accident? Perhaps it really was just worn out, as they had claimed. Still, I had a tiny hands puller (which is like a bearing puller, only much smaller), so I stopped the watch first by pulling the adjuster knob two clicks out, then took the third hand off, noting where it was sitting and being extremely careful not to touch the others. The hand itself is so tiny and thin that I was worried about wrecking it – it certainly wouldn’t take much to do that. Fortunately, my hands were still capable of some finesse, and I did all this while using my headset magnifier and a decent LED bench light; without those tools, I wouldn’t be able to see a thing! With the third hand now off, I could see it was a simple interference (friction) fit onto the shaft. There were no splines or flat sections for locating it, so it seemed a simple task to line it up properly and press it back into place, which is precisely what I did. When I’d stopped the watch, it was almost to the 18-­minute mark on the face, so I lined it up exactly with that, pushed the hand carefully home and restarted the watch. This time, the hand aligned perfectly, and I watched it go around a couple of times and saw the other hands responding at the correct times, so it must’ve been in the right place. I replaced the bezel and spring and ensured the crystal was clean before putting it back on. I didn’t want to be taking this section apart again. I also ensured the battery was installed correctly and seated – I didn’t want it losing time. I put the seals back into position and reinstalled the backplate. Having the right tools certainly makes this task much easier than trying to use a pair of pliers to grab hold of the indented areas on the back of the watch, all while not being able to hold it all steady. Australia's electronics magazine siliconchip.com.au It has been fine for months now, so hopefully, that’s the last time I’ll have to take it apart! Electron microscope vacuum pump repair M. C., of Leonards Hill, Vic runs a repair business that specialises in keeping unsupported and otherwise obsolete high-value equipment up and running (website at: www. technicalmayhem.com.au). Clients so far have mainly been universities, but he is hoping to expand into other fields. Here is the story of one repair undertaken... One Tuesday morning, I received a call from a major Melbourne university. One of their 1990s-era JEOL electron microscopes had developed a startup error after it had been left switched off over a long weekend. It was complaining that one of the vacuum pumps wasn’t starting. These microscopes are complicated beasts that take up a small room and require chilled water, several bottled gases and an extremely low vacuum inside the main unit. The vacuum system in this particular unit comprises five different pumps to achieve a high vacuum to avoid contamination of the sample or electron gun. In this case, the fault was reported to be in the second pump, a turbomolecular pump that looks similar to a truck turbocharger. Once I arrived, I confirmed that was the problem – the fault light on the rackmount pump controller was glowing red, and the user interface listed the fault in the startup sequence. Seiko Seiki in Japan manufactured the pump in question. Makers of complicated equipment like electron microscopes often use equipment from other manufacturers to avoid the huge expense of designing it themselves. These pumps run on a magnetic levitation bearing to achieve the super-low friction required to spin at up to 90,000RPM, undoubtedly a significant design challenge. The pump controller manual revealed that the fault light could be triggered by three different faults to do with the pump itself and one in the controller, unfortunately omitting any detail about how to narrow it down. The pump faults were the usual overspeed, underspeed, overload etc; the controller fault was a flat backup battery. This seemed easy – it must be a flat backup battery! However, the battery had been replaced recently and tested 100%. The battery is required in case the controller loses power without being shut down nicely, allowing the pump to spend a leisurely 15 minutes spinning to a stop on its frictionless magnetic bearings. I explained to the client the difficulty of troubleshooting the pump and controller unit without a schematic diagram or service manual. Still, such an investigation was probably the only reasonable course; a replacement was simply unobtainable. The pump and controller are matched to each other, and if they couldn’t be repaired, the alternative was a newer model pump and some work designing an interface to the microscope. We decided that the most reasonable course of action was to spend some time trying to diagnose the existing problem further. Opening up the controller case revealed many modules and PCBs squeezed neatly into the case. The front cover of the unit folded down to reveal a card cage with many PCBs that could be unplugged. The original service techs would have had a kit with an extender card for measuring test points and making adjustments, but I would have to improvise. siliconchip.com.au Australia's electronics magazine October 2023  93 I traced the fault LED wiring back to the card cage interconnecting backplane and onto a logic board with many 4000 series CMOS chips; a 4-input NOR gate drove the LED. This made sense; each input would indicate one fault. I couldn’t get the DMM probe into the unit with the PCB in the cage, so I soldered four numbered wires onto the gate inputs and re-inserted the card. With the unit powered up again, I checked each wire until I found the one sitting at +5V, narrowing the fault further. The input with the fault travelled off the board, back into the backplane and onto another PCB with a lot of analog circuitry onboard. The fault signal traced back to a comparator that measures the input of a voltage divider. Once again, I used the trick of soldering three numbered wires onto the top of the voltage divider and the two comparator inputs. The divider input measured 13.3V, with the comparator inputs measuring 0V and 2.47V. 13.3V seemed suspiciously like a fully charged 12V battery voltage – this was the backup battery voltage monitor circuit! What was going on? I removed the PCB again and measured the divider resistors. The lower measured 10.7kW while the upper, marked 47kW, measured open-circuit. This was the problem; a humble 0.25W resistor that looked perfect! All this was very strange, but I didn’t stop to think about it for too long; I quickly fitted a replacement. That fixed the controller; the system got through its startup sequence and the pump started. As the system crept towards its operating vacuum, I did a quick calculation. The result showed that the resistor should dissipate about 2.5mW in this application, roughly 1% of its rated maximum value. Don’t ask me to explain why it failed! Regardless, the client was very happy and there have been no more faults for several months. ATA automatic gate opener repair G. C., of The Gap, Qld went through quite a few trials rejuvenating a failed swinging gate controller. His story demonstrates how helpful it would be to have circuit diagrams of your equipment to help with repairs... 94 Silicon Chip Almost four years ago, I installed an ATA swing gate opener that used a 24V DC motor linked to a gearbox which transferred power to an articulated drive arm attached to the lower edge of the gate. The DCB-05 controller was mounted in its own plastic housing together with a solar controller board. A 30W solar panel was provided to charge the 24V 12Ah battery in a separate box. There were two failures in the first few months. One was caused by the normally-closed contacts of the limiting microswitches not making, and the other by an enormous ant infestation in the battery box, resulting in significant corrosion of the terminals and connectors. The gate was left open during a long renovation, and a large bush progressively enveloped the solar panel. When the renovations were finished, the gate opener was not working. However, the battery voltage measured 22V, which surprised me. The message on the controller’s LCD indicated that the limits needed to be set. I suspected that meant the battery voltage had dropped so low that the system required re-initialisation. I thought there was Buckley’s chance of the four-year-old lead-acid battery being salvageable, so I purchased a new pair of 12V 38Ah batteries. After installing the batteries, I was gobsmacked that when I went to re-initialise the controller, the display was showing gibberish with a continually changing pattern. Only a week before, it was perfect. What had happened? Was the microprocessor sending the display rubbish? If it was, there was no way I could fix it. I powered the control board directly from a 24V transformer (it accepted 24V AC or DC). When I looked closely at the display, I saw that the pattern was scrolling from left to right. When either the NEXT or PREVIOUS buttons were pressed, the unintelligible pattern remained stationary, and there was a confirmation beep. So, it was a fair bet that the LCD was faulty. Searching online, I found that Jaycar sold a display that was a close match and appeared to have the same pin-out. It was a discontinued line, selling at only $9. Within a day or so, I had purchased one, installed it, and it worked perfectly. Originally, double-sided tape had been used to adhere the display to its driver board. Prising them apart, I found a small area about 3mm in diameter of corrosion on the circuit board. The tape was so firmly stuck to the board that it was hard to see how any water/condensation, let alone an insect, could have gotten in there. There was no sign of corrosion anywhere else. After reinstalling the controller, when I tried to set up the limit switches, I got a “Limit Switch Not Activated” message every time. I found that the CLOSE microswitch was faulty. Fortunately, I had a spare with me, but substituting it made no difference. While the gate was closing, I could operate the microswitch manually, but the gate kept moving. I checked the wiring continuity from the microswitches back to the main board but found no problems. It looked like another fault in the control board! I also noticed that the battery voltage was dropping slightly, and when I measured the current from the solar controller to the battery, it was zero – not even a microamp. Clearly, this board was also faulty. Australia's electronics magazine siliconchip.com.au A close-up photo of the solar controller section of the gate controller. I emailed the manufacturer’s technical support guru. He responded quickly and said to ring him the next time I was on-site and he would lead me through setting up the limit switches. I followed his steps, conveying voltage readings to him. Unsurprisingly, he confirmed that both boards were faulty. He thought they might have been hit by lightning, but I could not see any evidence of that. He pointed out that it was possible to dispense with the microswitches by setting the controller to switch off the motor when the current started ramping up when an obstacle was encountered. I found that the limits for the controller could be easily set up by using large potted plants to constrain the gate’s travel. Returning to the main controller board, tracing the tracks from the terminal block, I found that the microswitch signals went through a resistor network and then a surface-mount IC. I could not find any data sheet, but I assumed it was a buffer. When I simulated the operation of the CLOSE and OPEN microswitches, I could see the output of this IC responding accordingly. Its outputs were connected to the inputs of the microprocessor by short tracks and there was no sign of corrosion. I did not try to look for these signals at the microprocessor as it was too risky; the multimeter probe was bound to short pins with my clumsy fingers. It was frustrating that I could not find any fault with the microswitches, the wiring or the main board. I noticed that the display was sometimes warning that “Service is due”. Being a born optimist, I set the service counter to 60,000 operations before this message would re-appear. It is doubtful that this service required warning would interfere with the operation of the controller, but I was not sure. Regardless, I was at the end of the road with this controller. Now the solar controller... I tried to “recondition” the recovered 24V battery using a smart charger, but it was too far gone. At least it charged to 24.4V, sufficient for testing the solar regulator. On the small solar controller board was an LM2588 adjustable flyback regulator that was delivering 27.3V after the output filter. The guru told me this module was designed to charge the battery at 27.5V, so that was close to the expected value. When I measured from the board ground (same as the solar panel negative) to the battery’s positive terminal, the reading was 27.3V. However, when I measured across the battery terminals on the board, the reading was 24.4V. Where had 2.9V disappeared? I found that a TO-220 package Mosfet (IRLZ44N) was between the board ground and the battery negative terminal, which was connected directly to the drain pin that siliconchip.com.au measured 2.9V. Its source pin was connected to ground and the gate to the battery’s positive terminal via a 1MW resistor. I therefore expected to measure 27.3V at the gate, but it was 0V; no wonder it was not conducting. I wasn’t sure of the purpose of this Mosfet; my friend said it was to protect the board in case the battery polarity was reversed. I note that no such precaution was taken with the solar panel. After removing the Mosfet, it appeared to test satisfactorily. However, it seemed to be a very strange circuit as the specifications of the Mosfet give a maximum allowable gate voltage of ±16V but, in this circuit, it appeared to be hit with 27.3V. I wondered if there was a breakdown between the gate and source terminals. Replacing the Mosfet with one with slightly better specifications, I found that the voltage measurements stayed the same. Removing the device from the board. I noticed a thin track from the gate terminal that disappeared under the edge of a large surface-mounted diode. I soon discovered that this track came out under the diode and led to a 1MW resistor in parallel with a capacitor to ground. At last, it all made sense. When I got a measurement of 1MW across the resistor, I was measuring through the switching regulator to ground with one probe and through the 1MW resistor, which was connected to ground with the other probe. Clearly, the 1MW resistor to battery positive was open-circuit. Unfortunately, this tiny resistor had doomed the battery. With the original Mosfet reinstalled and the open-circuit resistor replaced, the solar regulator was back in action. After reinstalling both boards, I attempted to set the system up using the microswitches to determine travel limits. The gate CLOSE limit was set immediately, but then the gate refused to open – no drive whatsoever. Now the normally-closed microswitch contacts for the gate OPEN limit were open-circuit. This second set of microswitches had also failed prematurely when the manufacturer’s specification was for an expected life of 200,000 operations. The metal enclosure for the motor/gearbox and microswitches did not have any sealing gaskets and, when I initially opened it, I was staggered to find a fair amount of sand and dirt inside. Perhaps the unlocked cover had not been put back properly, and sand, cement dust, sawdust etc had found their way into the box during the house construction. I think these contaminants must have compromised the microswitches. I didn’t waste any more time and set the limits using current sensing. The gate opener finally worked as it should. Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. Australia's electronics magazine October 2023  95 The downside of this method was that the gate closed and opened more slowly. Still, the troublesome microswitches were not needed, and the current to the motor was throttled back before the end stop, so the gate glided into the stop position without any clunk. Reviving an electric motor B. P., of Dundathu, Qld is a prolific repairer. This time he’s tackling an electric motor that he got for a song. It was in bad shape but just needed a bit of care before it was functional again... I was setting up a piece of equipment that used to be powered by a three-phase electric motor. I don’t have a three-phase supply here, so I decided to replace it with a single-phase ¾ horsepower (~550W) electric motor that I had picked up at one of the local tip shops. When I checked it, I found it was seized, so I dismantled it. It was difficult to get apart, but I eventually succeeded. It was obvious that the motor had been flooded at some stage because the rotor had a thick coat of rust, and the stator laminations weren’t much better. One bearing was utterly seized, and the other was not turning freely either. I started by removing the rust from the rotor and stator laminations with a rotary wire brush on my electric drill. I then tried to make the bearings usable so that I could test the motor before investing in new bearings. Both bearings were double-sealed, so I prised the seal off one side of each bearing. I sprayed them with lubricating spray and eventually got both running freely, so I oiled them. The bearings were not in a good enough condition to be reused but were good enough for testing, so I reassembled the motor. The good old electric motor shown in full along with the troublesome centrifugal switch contacts. 96 Silicon Chip I plugged the motor in and it tripped the safety switch after a quick flick of the shaft. I was not entirely surprised, as I’d previously worked on an irrigation pump with a leaking seal, which had caused the winding insulation in the stator to deteriorate and cause an Earth fault. I was about to scrap the motor when I decided to test the windings. There were four wires connected to a terminal block, so I removed them all, then got out my multimeter and turned it to the 20MW range. While this was not a Megger, it would at least give me an idea of where there might be an Earth fault. I tested each wire in turn and got no reading on any, so I turned my attention to the terminal block. I tested each of the four terminals, and one showed conductance to Earth. I thought that was strange, so I dismantled the motor to have a closer look at the terminal block. Behind the terminal block is a contact operated by the centrifugal switch, which switches in the capacitor to start the motor and then switches it out once the motor speed is high enough. I tested the terminal block, and I could find no fault with it, but I determined that the arms that ride on the centrifugal switch were slightly bent, which was causing them to contact the metal part of the rotor. I straightened the arms, reassembled the motor, and retested it for Earth faults. This time there was no fault, so I plugged the motor in again, and it sprang to life, but with a horrible bearing noise, which was no surprise. However, it was turning in an anticlockwise direction, whereas I needed it to turn in a clockwise direction. After unplugging it, I swapped over the two wires for the start winding and tried again. Now that the motor turned clockwise, it was time to see if I could fit it to the equipment. I removed the mounting bracket from the old motor, fitted it to the new one, and tried it on the equipment. The pulley did not align with the pulley on the equipment. I changed the bracket to the last two holes on the motor and the alignment was close enough that I would be able to adjust the position of the pulley on the shaft. But now, the bracket was only held on with two bolts. I dismantled the motor again to see if I could drill into the case to fit another two bolts. Luckily, there was enough clearance between the inside of the case and the windings on the stator to do that. I placed some timber between the windings and the case to avoid drilling into the windings. With new holes drilled and bolts fitted, the motor was ready to use after it got new bearings. I suspected I would have problems getting the bearings because when I measured them with my vernier caliper, they were both imperial sizes. Imperial bearings are now less common than metric. While shopping, my wife took them to the local Bearing Service in town but only returned with one new bearing. The shop got the other bearing for me in about a week, and after collecting it, I reassembled the motor. After a full service of the equipment and a few minor things replaced, I could use it again. The equipment now ran smoothly under heavy load with no indication of stalling. The replacement motor only cost me a few dollars, with $31 spent on new bearings, for a total of under $40. I was very happy with the outcome; an otherwise piece of useless scrap metal now had a new purpose in life. SC Australia's electronics magazine siliconchip.com.au A selection of our best selling soldering irons and accessories at great Jaycar value! 25W Soldering Iron TS1465 $19.95 Build, repair or service with our Soldering Solutions. We stock a GREAT RANGE of gas and electric soldering irons, solder, service aids and workbench essentials. 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Jaycar reserves the right to change prices if and when required. Vintage Radio The Imperial Japanese Army (IJA) Chi Receiver By Ian Batty Hats off to the fossicker who asked me to look at this unexpected treasure: a “Chi” ground receiver designed and made in Japan during the Pacific Campaign of World War II. I have previously mentioned that unique class of collectors – the ones who discover and work to preserve items most of us would pass by, or never even dream of finding. It’s thanks to them that I can document this rare find. I must also thank the founder of the Yokohama WWII Japanese Military Radio Museum, Takashi Doi, for providing the circuit diagram and background information (see www.yokohamaradiomuseum.com). Before we get to the Chi, first we must look at the landmark HRO design by the National Radio Company of Malden, MA, USA (not to be confused with National Panasonic of Japan). Collectors of communications receivers will know of it. Its seemingly-­ conservative design became the standard by which others were judged, and the standard to beat. 98 Silicon Chip It’s a design that inspired many other manufacturers: two RF stages, a converter with a separate local oscillator (LO), two intermediate frequency (IF) stages, a demodulator/AGC/first audio stage and an audio output stage. Looking at the converter stage, those of us used to multi-grid or multi-­ section converters (pentagrids or triode-­ hexodes) might wonder why the HRO used a simple pentode converter with a separate local oscillator. The HRO was first advertised in 1934, only one year after the patent was awarded for the pentagrid. While this single-tube converter worked adequately at broadcast frequencies, it was noisy, and its performance at higher frequencies was poor. Improved converters such as the triode-hexode would not be announced until 1935. Given National’s prominence as a Australia's electronics magazine supplier of top-quality receivers, and the lead time from design to release, James Millen, Herbert Hoover Jr and Howard Morgan would naturally incorporate the well-known, reliable pentode mixer into the HRO. Hoover and Morgan, designers of the electronics, opted for LO injection to the screen grid. In common with all other multiplicative mixers, this pushed the valve’s electron stream to cut off at the most negative part of the LO’s signal. This Class-B operation is vital to the superhet’s converter action. Our own Kingsley AR7 uses a similar design overall but substitutes the triode-hexode 6K8/6K8G (using an internal LO) as a converter stage. By the way, Hoover set up a lab in his garage, employing Howard Morgan from Western Electric Co and a few of his technicians to develop the siliconchip.com.au The rear view of the Chi Mark 1 chassis. From left-to-right are the first IF transformer, IF1 (#52, 6D6), second IF transformer, IF2 (#61, 6D6), demodulator/ AGC stage (#74, 6B7) and audio output valve (#104, 6C6). new receiver circuitry. It’s a tradition repeated by Bill Hewlett and David Packard in 1938, revived almost four decades later by Steve Wozniak and Steve Jobs of Apple fame. Similar designs, with two RF stages, were also used in the MN-26, AN/ ARN-6 and AN/ARN-7 aircraft radio compass receivers. The Chi (地) The Director of the Yokohama WWII Japanese Military Radio Museum kindly sent me the following description: In 1939, the Imperial Army formalised the Chi Mark 1-4 Radio Sets as the new ground-use radio equipment for the Air Force under the 4th formalisation work. The name Chi (ground) denotes ground-based anti-aircraft use. Chi Transmitter Mark 1 The Chi Mark 1 transmitter’s output power was 1kW (A1/CW). The companion receiver was a superheterodyne type, described below. The receiver was known as the Chi Mark 1 Radio Set/Receiver. The full name in (pre-WW2) Japanese was written as: 地一號受信機（に型）接續要圖 The receiver covered 140-13,350kHz using eight plug-in coil sets. An improved version was quickly introduced, covering 140-20,200kHz with nine coil sets. The receiver constituted the topof-the-line radio equipment for the Army’s field aviation units. But they were very laborious to manufacture, entirely unsuitable for mass siliconchip.com.au production, and expensive. Soon after the outbreak of the Pacific War, a large number of receivers were required for operations such as ground-to-air and base-to-base communications and intercepting enemy communications. The introduction of high-performance general-purpose receivers was requested. For this reason, the Mark 1 radio set/receiver was greatly simplified and made suitable for mass production as the Chi Mark 1 version. There was no significant difference in performance between the two receivers, and while the weight of the Chi Mark 1 radio set/receiver was 17kg, the revised Chi Mark 1 receiver was much lighter at 13kg. The set is a superheterodyne fitted with a beat frequency oscillator (BFO), automatic gain control (AGC), two stages of RF amplification, two stages of IF amplification and two stages of AF amplification. The receiving frequency covers 140~20,000kHz in nine bands, using plug-in coil sets. Depending on the frequency range, the IF is either 65kHz (receiving frequency 140~1,500kHz) or 450kHz (receiving frequency 1,500~20,000kHz), although some sources say that it should be 456kHz. The IF is changed by swapping four internally-located IF units (first IF, second IF, final IF pair, BFO). The set features a narrow-band crystal filter for the 450kHz IF, which is inoperative for the 65kHz IF. The entire design is similar to the HRO but with notable differences explained below. Tuning dials One of the HRO’s outstanding features was its patented precision dial, quoted as being the equivalent of a ‘four-foot [122cm] slide rule’. This was repeated on the AR7, but one wonders how useful it was. Ray Robinson’s AR7 review is worth reading on the matter (www.tuberadio.com/robinson/ museum/AR7/). The HRO’s calibration reportedly demanded four hours to make up the calibration charts for all four coil boxes. Calibration readings were transcribed to an individual printed scale for each coil box. Unlike the HRO and the AR7, the Chi has a simple 0-100 dial, with (like the HRO/AR7) a hand-drawn 160 × 20mm calibration chart for each coil box. The calibration chart for the Chi Mark 1 receiver. Note that the model number on this chart (40757) is different from the front panel (40780). Australia's electronics magazine October 2023  99 For the Chi, the accepted visual-­ reading accuracy of plus or minus half an intermediate division gives an accuracy of about ±15kHz in the 2.5~5MHz range. The HRO and AR7 used similar hand-drawn scales, so their precision vernier dials may not have contributed any greater indication accuracy than the Chi’s simple 0-100 dial. Circuit description The circuit (Fig.1) simply numbers components in order, similar to our Astor sets. I have kept the original numbering for consistency. The circuit supplied by the Yokohama Museum was happily clear, with all notations readable, although I have redrawn it for greater clarity. I have also redrawn the demodulator stage for ease of interpretation and description. The antenna circuit, comprising coil box sets #4a/#4b, is tuned by the first section of the four-gang tuning capacitor (#6, #17, #30 & #39). Antenna selector switch #2 connects directly to antenna socket #1a (short antenna), via matching capacitor #121 (long antenna) or to ground. There’s also a direct connection to the first RF amplifier grid via socket #1b and capacitor #120. The two RF stages are similar to those of the HRO. Both valves in the Chi are remote cutoff UX6-based UZ-6D6s, similar to the later octal 6U7. UZ is a Japanese coding; in this case, it refers to a valve with a standard longpin six-pin base. Both RF stages have AGC applied, the first (confusingly designated RF2) via 500kW resistor #23 and the second (designated RF1) via 500kW resistor #18. Bypassing is done by 10nF capacitors #7 and #19. The first RF stage operates with fixed bias derived across 300W resistor #9, bypassed by 10nF capacitor #10. The second RF stage cathode returns to ground via 300W cathode bias resistor #21 (bypassed by 10nF capacitor #22), then via the set’s 10kW RF/IF gain control potentiometer, #91. This pot also controls both IF amplifiers. The 6D6 (and 6C6) are ‘triple-grid’ amplifiers, with the suppressor grid bought out to its own pin connection on the six-pin base and wired externally to the cathode. The first RF has its own screen supply via 100kW resistor #11, bypassed by 10nF capacitor #12. The second RF shares a common screen supply with both IF amplifiers, individually bypassed by 10nF capacitor #25. That supply is derived from a voltage divider of resistors #89 (30kW) and #90 (50kW) plus RF/ IF gain pot #91 (10kW). Inductors #93 and #94 provide RF decoupling along with bypass capacitors #25, #55 and #64 (all 10nF). Making the RF/IF gain control part of a voltage divider gives more predictable gain control than the simpler cathode-circuit-only alternative. The RF amplifiers drive coil box RF transformers #15a/#15b (first RF) and #28a/#28b (second RF) with untuned primaries and tuned secondaries. Each RF amplifier is decoupled from HT by 3kW resistors and 10nF capacitors (#11/#14 and #26/#27). Unusually, the antenna and RF coil boxes only contain inductors; there are no internal trimmer capacitors. Frequency alignment for coils #4b, #15b and #28b (antenna, RF interstage and mixer grid) is by individual variable capacitors (#5, #16 and #29). These are all mounted on the front panel and allow individual adjustments of their circuits. Notice that these capacitors are drawn as variable (operator-­adjustable) and not preset (workshop-­adjustable). Given the Chi’s intended use, from military command centres to battlefield deployment, and the difficulty of guaranteeing alignment in such a wide range of environments, it made sense to give trained operators the ability to optimise front-end alignment in any situation. It can also be confusing; more on that later. The Chi’s ‘all-tuneable’ design may highlight a difference between the US military and the IJA. The US Army enlisted tens of millions, was able to train and assign many for support roles such as radio technicians, and could afford to set up local depots and repair shops close to (or on) battlefields. The IJA, by contrast, was engaged in rapid forward offensives until about late 1943, when the tide of war turned against them. Troops in forward deployments often had little in terms of advanced technical support. The military demand of ‘work first time, work all the time, work anywhere’ Fig.1: a redrawn circuit diagram of the Chi Mark 1 receiver. The scale is unfortunately a bit small but that’s necessary to get everything into the available space. There are nine valves shown here; the tenth is a rectifier in the power supply (see Fig.3). 100 Silicon Chip Australia's electronics magazine siliconchip.com.au was met by giving operators the most flexible equipment possible. The Chi uses a pentode mixer, but unlike the HRO, it uses suppressor injection. As the suppressor was designed to correct the secondary emission problem in tetrodes, it has a pretty open spiral construction. This means that it needs considerable negative bias to cut a valve off. In the case of the famous EF50, suppressor cutoff demands some -50V of bias. The mixer valve (#31) is a sharp cutoff UX6-based 6C6, identical to the later octal 6J7. Because of its sharp cutoff characteristics, it does not have AGC applied and is not affected by the RF/IF gain control. This stage works with very low supply voltages, only about 20V. This had me checking and double-­ checking my measurements. Remember that mixer action relies on cutoff for the most negative part of the LO signal. Such low voltages would ensure that the suppressor-injected LO signal does drive the valve into the cutoff region as required. The screen grid has a much greater effect on anode current; the HRO, using screen injection, could apply more normal supply voltages to its pentode mixer and still ensure the required anode current cutoff. As noted above, the AR7, coming some years later when high-performance triode-hexodes were available, solved the problem by using the 6K8/6K8G. The LO (#42) also uses a 6C6 in a cathode-coupled Hartley circuit. siliconchip.com.au Although the valve is supplied with the usual anode and screen voltages, these are both bypassed to signal ground. Feedback is from the cathode to the grid. As the circuit is a cathode follower with feedback, there is zero phase shift, and the voltage gain is less than unity. That means the circuit can use a single tuned winding with no phase inversion, and the tuned circuit gives a voltage step-up from the cathode to the grid to establish oscillation. This circuit became the preferred design in 6SA7/6BE6 pentagrid converter circuits. The selected coil box’s coil (#38a) is tuned by the LO section of the tuning gang, #39. The LO coil box does contain a workshop-adjustable trimmer (#38c), as the LO’s accuracy determines the set’s frequency calibration. There is no operator adjustment for LO calibration. Each LO coil box contains a padder (#38b) to ensure the LO tracks by the IF value above the incoming signal. Any minor tracking errors between LO and the antenna/RF circuits are corrected by the operator’s use of the three manual trimmers in the antenna/RF stages. The mixer feeds the first IF valve via first IF transformer #49b~#49e, tuned for 450kHz. The transformer’s tuned primary and secondary use fixed capacitors and inductance tuning. The first IF amplifier (#52), a remote cutoff 6D6, is biased by fixed 300W resistor #53, bypassed by 10nF capacitor #54, Australia's electronics magazine and then connects to ground via the common 10kW RF/IF gain potentiometer, #91. The second IF amplifier’s (#61) biasing and bypassing are similar. The second IF feeds the input section of the final IF’s bandpass assembly #67g~#67k. The signal is then fed to the switchable crystal filter #68a~#68c, described more fully below. The signal from the crystal filter passes to the output section of the final IF bandpass filter, #67m~#67q. Its output secondary feeds the demodulator (lower) diode in #74, the demodulator/ AGC/first audio valve, a Ut-6B7 (Ut is another Japanese prefix). An IF signal is fed, via 1nF capacitor #69, to the Ut-6B7’s (upper) AGC rectifier diode. AGC is developed across 500kW resistor #86, filtered by 500kW resistor #87 and 10nF capacitor #88, and applied to the two RF and two IF stages. For A1/CW operation, the AGC is disabled by one section of CW/ AM switch #101. A1/CW operation is described below. The 6B7’s cathode return comprises resistors #79 (1kW) and #78 (3kW). A cathode bias of around 2V is developed across resistor #79, with the grid returning to the junction of resistors #79 and #78 via 500kW resistor #75. The demodulator diode returns to the 6B7 cathode. This means it has no bias and will respond to all IF signals. Its cathode current develops another 5.7V across the bottom cathode resistor, #78. Since the AGC diode returns to ground, the drop across #78 is also October 2023  101 (see Fig.3). The supply included an AC voltmeter, allowing operators to set the correct mains voltage. For battery operation, the Chi used a motor-generator set, also known as a ‘dynamotor’ or ‘genemotor’, to convert the low DC voltage from a battery into the required ~200V DC HT voltage. It is basically a DC motor driving a generator. In this case, it is a conventional 6V DC to 200V DC unit with the usual extensive primary and secondary filtering (also shown in Fig.3). Getting it going The top view of the chassis (right-to-left), primarily showing the 1st RF amp, 2nd RF amp, tuning, gear drive, mixer local oscillator tuning and crystal filter. the AGC delay voltage. At around 6V, it seems high, but this radio was designed for weak-signal performance, so it needs such a delay to prevent gain reduction for microvolt-level signals. Demodulated audio is fed via 10nF capacitor #70 and 500kW resistor #77 to the 6B7’s pentode grid, which returns to the cathode bias point (#79/#78) via 500kW grid return resistor #75. The cathode resistors are bypassed by 10nF capacitor #73; other minor components in this part of the circuit include #71, #72 and #76. The 6B7’s screen is supplied via resistors #82 (two 100kW resistors in series) and #81, bypassed by 10nF capacitor #80. The audio signal is developed across load resistor #85 (decoupled by #84 and #83) and fed to the output stage grid via 1nF capacitor #102. Output valve #104, a 6C6, drives output transformer #112. It feeds the two headphone jacks, #114, and its screen is supplied via 100kW resistor #107, with 10nF bypass #108. BFO and crystal filter For A1/Morse code/continuous wave (CW) reception, the set uses a beat frequency oscillator (BFO), built around another 6D6 (#97). This produces a tuneable signal that can be offset from the received IF signal, making unmodulated transmissions audible – 1kHz is a common choice. It can also resolve single sideband (SSB) voice signals. 102 Silicon Chip It’s a cathode-coupled Hartley oscillator, and its output is fed to the demodulator diode. The diode acts as an additive mixer, producing a tone with a frequency that’s the difference between the IF signal frequency and the BFO frequency. The main IF channel’s bandwidth is around ±1.8kHz. This is necessary for voice reception, but a narrower bandwidth can be used for CW. Narrowing the bandwidth has the advantage of improving the signal-to-noise ratio, as a channel’s noise is proportional to the square root of its bandwidth. The crystal filter (#68a~c) exploits the very high Q of a quartz crystal (20,000+). This implies a very narrow filter bandwidth. In operation, crystal #68b is shunted by variable capacitor #68c, allowing the filter bandwidth to be adjusted. For voice reception, the filter is taken out of circuit by switch #68a. Regrettably, this set’s crystal was marked 400kHz, rather than the required value of 450kHz. While this prevented the filter from being tested, it seemed to be an original fitting – it was certainly in the correct holder. A factory error? We’ll probably never know. Power supply The Chi needs 6V (AC or DC) for the heaters and +200V DC for HT. The AC mains supply operated from 80~120V AC or 200~240V AC input, using a KX-80 in a conventional fullwave circuit with a two-section pi filter Australia's electronics magazine I took charge of this set in early 2019 but didn’t have much luck getting it going, so I returned it to the owner. He contacted fellow HRSA member Brian Goldsmith and asked him to look at it. Brian found numerous problems. Firstly, some valves were not functioning correctly. Brian resoldered all of their bases, and they came back good. Many of the 450kHz coils (IFs and BFO) were loose, so he fixed them in place using paraffin wax rather than using superglue or some kind of resin. This holds them in place but permits later disassembly if needed. The tuning system comprised two dual-gang variable capacitors linked by the central gear drive and a drive sleeve. The left-side sleeve was loose, creating backlash when tuning, and the locating bearings at each end of the two-gang sections were also loose, so all moving plates were not correctly located relative to the fixed plates. Once repaired, the tuning mechanism worked perfectly. The audio output transformer was faulty, so he replaced it with the closest match available. He then performed an alignment, only to find that some of the ferrite adjusting cores were loose. If, after doing the alignment, you turn the set upside-down and the alignment changes, something is loose inside the coil cans. The crystal in the crystal filter was confirmed as 400kHz, and Brian could not find a replacement. Finally, the BFO was inoperative. The circuit resistances and voltages appeared correct, and the fault could not be fixed. The radio came back to me a bit later. Once on the bench, I confirmed all the valves as being good. A quick check of DC voltages showed them as expected, so it was on to signal tracing siliconchip.com.au and testing. The IF and audio sections worked as expected, but the RF section was dead. After some faffing about, I discovered the three manual trimmers (Antenna/first RF/second RF). Adjusting these correctly brought the set to life. It was sensitive, but not as good as I expected. I went over the IF again and found I needed a lot of signal at the final IF grid. Checking the last IF, I adjusted the secondary core to each end of its travel without finding any peak. Removing the assembly from its can, I found the primary peaking at just on 500kHz – it was well above the correct figure of 450kHz, due to being out of the aluminium can with its capacitive and inductive effects. This indicated that the primary was OK and hinted that the secondary would have to peak around the same point, about 500kHz. I couldn’t easily get the secondary to peak with my grid dip oscillator on its 500kHz~1.5MHz range. Connecting it to a signal generator and oscilloscope showed why – it peaked at around 350kHz! 100pF tuning capacitor #67q measured high at around 120pF, so I put in a new 100pF capacitor. The coil would still not reach the 500kHz that was needed from the can. I ended up with only 47pF for #67q. Why? The protective wax may have contributed extra capacitance with age. Whatever the cause, reassembling and reinstalling the final IF, then aligning it, brought the set to life. Although noisy, it could easily respond to signals around 1μV at 5MHz. The BFO superpower As described above, the BFO is a simple cathode-coupled Hartley oscillator with electron coupling for the output to the demodulator. It wasn’t working even though the valve tested good. The DC voltages were also acceptable, and the tuning coil resistances looked fine. I disassembled the coil can and checked again. In desperation, I disconnected and measured the internal 150pF tuning capacitor, which came up at 148.5pF. While doing this, one lead on the 50kW grid leak resistor broke off close to the resistor body. The lead connecting the two capacitors to the top of the coil also parted as I worked on the assembly. The resistor itself measured 54kW. I repaired the broken leads and, after reassembly and adjustment, the BFO worked perfectly. I suspect that one of the parted leads had been minutely fractured, and that had been the problem – I’d certainly not seen any evidence of clean breakages. BFOs were originally designed to make unmodulated (CW) transmissions more detectable. With no modulation, all you hear (maybe!) is a series of clicks as the carrier cuts in and drops off. The BFO is essential to the intelligibility of the widely-used SSB communication mode, replacing the carrier that was removed by the transmitter. What’s not so obvious is the increase in sensitivity that the BFO can give. In the Chi, I could easily detect an unmodulated signal of only 200nV at 9MHz. It was usable but noisy. Such a signal would likely be below the general noise floor that bedevils all HF communication. So it’s an impressive superpower, if you can actually use it. How good is it? Its absolute sensitivity, for 1mW The underside of the chassis is neatly presented with nearly every (!) component numbered as per the circuit diagram shown in Fig.1. The chassis provides ample room for each component, making servicing a breeze. siliconchip.com.au Australia's electronics magazine October 2023  103 into headphones, ranges from 12.5μV at 4.5MHz and 9.3μV at 2.5MHz, to 0.45μV at 9MHz and 1.1μV at 5MHz. The signal-plus-noise-to-noise ratios (S+N:N) are 20dB at 4.5MHz and 2.5MHz, but only 2dB at 9MHz and 3dB at 5MHz. Dial calibration was within about 1% across the bands. Opening the 2.5~5MHz LO can showed that the calibrating trimmer had probably not been touched since decommissioning. That’s impressive for equipment that has likely been idle for over 70 years. It’s also a reminder that it is worth attempting to restore and preserve all well-built equipment, whether military or civilian. I’ve plotted the dial calibrations and signal performances in Fig.2. The well-known calculation for noise figure resolves handily for a 50W source: a noise voltage of 1nV multiplied by the square root of system bandwidth in hertz. Even a perfectly noiseless receiver with a bandwidth of 3.7kHz would have a noise floor of about 60nV. Valves such as the 6D6 have equivalent noise resistances in the kilohms range. While a full discussion is outside the scope of this article, it’s easy to see why signals much less than 10μV will necessarily have poor signal-tonoise ratios. Having a super-sensitive set is one thing, but there are two reservations. Firstly, atmospheric noise at MF/HF (300kHz to 30MHz) can easily reach the equivalent of 10μV. When exposed to such a high noise floor, the most sensitive receiver won’t be much better than any good set. Secondly, a raw figure of 1μV is pretty useless if the set’s S+N:N ratio Selectivity/ Xtal Filter On/Off BFO Tune AM/CW (A3/A1) 2nd RF/Converter Tuning 1st RF Antenna Tuning Tuning Antenna Matching RF/IF Gain Tuning Headphone Sockets Off/Standby/On Antenna Input Ground Direct Input Plug-in Coil Box (2500-4700kHz) A labelled shot of the front panel. Judging from the metallic tag, this radio was produced by the Anritsu Corporation. means that signals are unintelligible due to high internal noise. Ordinary pentodes are pretty noisy, and the noise generated in the first stage will determine any receiver’s ultimate sensitivity. The IF bandwidth is about ±1.85kHz at -3dB and ±14kHz at -60dB. Audio response from the antenna to the headphones is 500~3500Hz at -3dB, with a rapid roll-off below 500Hz. The set is intended for headphone use, so all tests were done at 1mW output. It can deliver around 60mW maximum, enough for a loudspeaker in quiet settings. AGC action is complicated by the RF/IF gain control setting. Generally, a 6dB output rise happened with only a 20dB input rise; that is certainly not as good as common domestic superhets. However, it needed over 100mV to overload at full gain. In practice, very powerful signals can be managed by a combination of RF/IF gain control and detuning one or more of the RF stages. The two RF stages give good IF and image rejection. IF rejection at 5MHz was around 93dB and image rejection around 75dB. Evaluation The set’s build quality is excellent. Despite its complex design, getting to all the test points was easy. Virtually every component is individually branded with its circuit number. This made locating components very simple, in contrast to the more common method where parts only carry their electrical values that are often either difficult to read or obscured by being mounted upside down. Under my RMA criteria, it gets a 10 for maintainability. The circuit diagram is excellent, and the parts list denotes not only most components’ electrical values but also their function in the circuit. #10, for example, is fully described as the “First high-­ frequency amplifier tube cathode capacitor (0.01μF)”. Such descriptions are valuable in the workshop – you can find out what Fig.2: a plot of the dial calibrations and signal performances at various frequencies. 104 Silicon Chip Australia's electronics magazine siliconchip.com.au 號 b c           a b c d e f         a b c d e f         a b     3    4 F 1 5  E  2   3  2     1 6 5 6 E 6    1 +6V +6V  2  –  3 4     1µF       10nF    10nF      0.1mH 1  Mechanical Genemotor 10nF 2 1µF3 4  +200V +6V     6mH +200V +200V 1  3 +6V +6V  – 4  – 2   2 x 10µF  100mA 100V 交流電源 100200V 2 5060C/S 3  1A  KX-80  +20V   1µF      1 2 3 4     +200V +6V 1 7  2   3 4  +2 +6   +20V 0 4     1 4   100V 交流電源 100200V 2 5060C/S 3  30H 30H  200V  1  200V 10µF   100mA 6mH 3.5H 3.5H 10µF  150V AC Generator 100~200V 50~60Hz/s  0.1mH  30kΩ    0 -20V 8 -20V Fig.3: the power supply section of the ‘original’ circuit diagram, courtesy of Takashi Doi (Yokohama Radio Museum; www. 名 稱 諸 元 番號 名 circuitry 稱 元 番號 名 稱 (#208) and 諸 元 番號 rectifier 名 valve 稱 yokohamaradiomuseum.com). This uses a 諸mechanical genemotor KX80 (#310). 諸 元 1μF c 欠  音量調整器側路蓄電器  電池接栓受 第一局部發振管同調直列蓄電器 番 諸 元 番號 名 稱 第一局部發振管同調並列蓄電器 b 第一局部發振管同調直列蓄電器 第一局部發振管同調蓄電器 c 第一局部發振管同調並列蓄電器 50kΩ (D-05型) 第一局部發振管格子抵抗器  第一局部發振管同調蓄電器 0.00025μF 第一局部發振管格子蓄電器  第一局部發振管格子抵抗器 UZ-6C6 第一局部發振管  第一局部發振管格子蓄電器 3kΩ (D-05型) 第一局部發振管陽極直列抵抗器 甲  第一局部發振管 30kΩ (D-05型) 第一局部發振管遮蔽格子分圧抵抗器 甲  第一局部發振管陽極直列抵抗器 甲 100kΩ(D-05型) 第一局部發振管遮蔽格子分圧抵抗器 乙  第一局部發振管遮蔽格子分圧抵抗器 0.01μF甲 第一局部發振管陽極側路蓄電器 甲  第一局部發振管遮蔽格子分圧抵抗器 0.01μF 0.01μF乙 第一局部發振管陽極側路蓄電器 乙  第一局部發振管陽極側路蓄電器0.01μF UZ-6D6 甲 第一局部發振管遮蔽格子側路蓄電器  第一局部發振管陽極側路蓄電器 乙 300Ω (D-05型) 欠 番  第一局部發振管遮蔽格子側路蓄電器 0.01μF 變周管陽極同調蓄電器 番 100kΩ (D-05型) a 欠 變周管陽極同調線輪 b 變周管陽極同調蓄電器 0.01μF 第一中間周波増幅管格子同調線輪 3kΩ (D-05型) c 變周管陽極同調線輪 第一中間周波増幅管格子同調蓄電器 d 第一中間周波増幅管格子同調線輪 0.01μF 欠 番 e 第一中間周波増幅管格子同調蓄電器 第一中間周波増幅管格子直列抵抗器 500kΩ (D-05型) f 欠 番 第一中間周波増幅管格子側路蓄電器 0.01μF  第一中間周波増幅管格子直列抵抗器 第一中間周波増幅管 UZ-6D6  第一中間周波増幅管格子側路蓄電器 第一中間周波増幅管陰極直列抵抗器 300Ω (D-05型) 500kΩ (D-05型)  第一中間周波増幅管 第一中間周波増幅管陰極側路蓄電器 0.01μF X2  第一中間周波増幅管陰極直列抵抗器 0.01μF 第一中間周波増幅管遮蔽格子側路蓄電器 0.01μF  第一中間周波増幅管陰極側路蓄電器 UZ-6D6 第一中間周波増幅管陽極直列抵抗器 3kΩ (D-05型) 300Ω (D-05型)  第一中間周波増幅管遮蔽格子側路蓄電器 第一中間周波増幅管陽極側路蓄電器 0.01μF  第一中間周波増幅管陽極直列抵抗器 0.01μF 欠 番 500kΩ (D-05型)  第一中間周波増幅管陽極側路蓄電器 第一中間周波増幅管陽極同調蓄電器 a 欠 番 0.01μF 第一中間周波増幅管陽極同調線輪 b 第一中間周波増幅管陽極同調蓄電器 0.01μF 第二中間周波増幅管格子同調線輪 3kΩ (D-05型) c 第一中間周波増幅管陽極同調線輪 第二中間周波増幅管格子同調蓄電器 d 第二中間周波増幅管格子同調線輪 0.01μF 欠 番 e 第二中間周波増幅管格子同調蓄電器 第二中間周波増幅管格子直列抵抗器 500kΩ (D-05型) f 欠 番 第二中間周波増幅管格子側路蓄電器 0.01μF  第二中間周波増幅管格子直列抵抗器 第二中間周波増幅管 UZ-6D6  第二中間周波増幅管格子側路蓄電器 第二中間周波増幅管陰極直列抵抗器 300Ω (D-05型)  第二中間周波増幅管 UZ-6C6 第二中間周波増幅管陰極側路蓄電器 0.01μF 5kΩ (D-05型)  第二中間周波増幅管陰極直列抵抗器 第二中間周波増幅管遮蔽格子側路蓄電器 0.01μF  第二中間周波増幅管陰極側路蓄電器 0.01μF 第二中間周波増幅管陽極直列抵抗器 3kΩ (D-05型) 3kΩ (D-05型)  第二中間周波増幅管遮蔽格子側路蓄電器 第二中間周波増幅管陽極側路蓄電器 0.01μF  第二中間周波増幅管陽極直列抵抗器 0.01μF 欠 番 500kΩ 番 (D-05型)  第二中間周波増幅管陽極側路蓄電器 欠 番 100kΩ (D-05型) a 欠 b 欠 番 E F G d e f g h i j k l m n o p q r a b c                        諸 番元 番號 名 稱  欠 c 欠 番  欠 番 d 欠 番 a 欠 番 e 欠 番 b 第二中間周波増幅管陽極結合線輪 (二号) 50kΩ (D-05型) f 欠 番 c 水晶濾波器入力側同調線輪 (二号) g 甲 0.00025μF 第二中間周波増幅管陽極結合線輪 (二号) d 水晶濾波器入力側同調蓄電器 (二号) h UZ-6C6 水晶濾波器入力側同調線輪 (二号) e 欠 番 3kΩ (D-05型) i 乙 水晶濾波器入力側同調蓄電器 甲 (二号)  水晶濾波器入力側同調蓄電器 (二号) 30kΩ (D-05型) j 丙 欠 番  水晶濾波器入力側同調蓄電器 (二号) 100kΩ(D-05型) k 水晶濾波器入力側同調蓄電器 乙 (二号)  水晶濾波器平衡蓄電器 (二号) l 水晶濾波器入力側同調蓄電器 0.01μF 丙 (二号)  水晶濾波器出力結合蓄電器 (二号) m 水晶濾波器平衡蓄電器 0.01μF (二号)  水晶濾波器出力結合線輪 (二号) n 水晶濾波器出力結合蓄電器 0.01μF (二号)  Ut-6B7検波陽極同調線輪 o 水晶濾波器出力結合線輪 (二号)  Ut-6B7検波陽極同調蓄電器 p Ut-6B7検波陽極同調線輪  欠 番 q Ut-6B7検波陽極同調蓄電器  水晶濾波器轉換器 r 欠 番  水晶共振子 a 水晶濾波器轉換器  選擇度調整器 b 水晶共振子  Ut-6B7検波陽極結合蓄電器 0.001μF 500kΩ (D-05型) c 選擇度調整器  Ut-6B7検波陽極低周波結合蓄電器 0.01μF  Ut-6B7検波陽極結合蓄電器 500kΩ (D-05型)  0.01μF Ut-6B7検波陽極抵抗器  Ut-6B7検波陽極低周波結合蓄電器 UZ-6D6  Ut-6B7検波陽極側路蓄電器 0.00025μF  300Ω (D-05型) Ut-6B7検波陽極抵抗器  Ut-6B7陰極側路蓄電器 0.01μF  Ut-6B7検波陽極側路蓄電器 0.01μF X2  第二検波並第一低周波増幅管 Ut-6B7  Ut-6B7陰極側路蓄電器 0.01μF Ut-6B7格子抵抗器 500kΩ (D-05型)  3kΩ (D-05型)  第二検波並第一低周波増幅管 0.00025μF  Ut-6B7格子低周波側路蓄電器  Ut-6B7格子抵抗器 0.01μF Ut-6B7格子直列抵抗器 500kΩ (D-05型)   Ut-6B7格子低周波側路蓄電器3kΩ (D-05型)  Ut-6B7陰極直列抵抗器 甲  Ut-6B7格子直列抵抗器 Ut-6B7陰極直列抵抗器 乙 1kΩ (D-05型)   Ut-6B7陰極直列抵抗器 甲  Ut-6B7遮蔽格子側路蓄電器 0.01μF  Ut-6B7陰極直列抵抗器 乙 100kΩ (D-05型)  Ut-6B7格子分圧抵抗器 甲  Ut-6B7遮蔽格子側路蓄電器 Ut-6B7格子分圧抵抗器 乙 100kΩX2(D-05型)  1μF  Ut-6B7陽極側路蓄電器  Ut-6B7格子分圧抵抗器 甲  Ut-6B7格子分圧抵抗器 乙 3kΩ (D-05型) 500kΩ (D-05型) 甲 Ut-6B7陽極直列抵抗器  Ut-6B7陽極側路蓄電器 0.01μF Ut-6B7陽極直列抵抗器 乙 100kΩ (D-05型)  Ut-6B7陽極直列抵抗器 甲 500kΩ (D-05型) UZ-6D6 Ut-6B7検波陽極自動音量調整抵抗器 300Ω (D-05型)  Ut-6B7陽極直列抵抗器 乙 500kΩ (D-05型) Ut-6B7検波陽極自動音量調整濾波抵抗器  Ut-6B7検波陽極自動音量調整抵抗器 0.01μF Ut-6B7検波陽極自動音量調整側路蓄電器 0.01μF 0.01μF 遮蔽格子分圧抵抗器 甲  Ut-6B7検波陽極自動音量調整濾波抵抗器 30kΩ (D-2型) 3kΩ (D-05型)乙  Ut-6B7検波陽極自動音量調整側路蓄電器 遮蔽格子分圧抵抗器 50kΩ (D-2型)  遮蔽格子分圧抵抗器 甲 音量調整器0.01μF 10kΩ  遮蔽格子分圧抵抗器 乙  音量調整器 I H J a component does without having to read the manual. It’s also notable for having a minimal list of component values. RF bypass capacitors are overwhelmingly 10nF in value. Most resistors are 1kW, 3kW, 50kW or 100kW. Such a design adds to the Chi’s serviceability, as technicians only need to keep a small inventory of spare components for repair. Aside from the 7-pin 6B7 demodulator/AGC/first audio valve, it would be possible to put any 6-pin pentode valve in any 6-pin socket and have a working set. Conclusion There are very few of these exceptional radios still in existence, and this D E F G 諸 元 番號 名 稱 第二高周波増幅管遮蔽格子塞流線輪  音量調整器側路蓄電器 第一中間周波増幅管遮蔽格子塞流線輪 第二局部發振管同調線輪  第二高周波増幅管遮蔽格子塞流線輪  第一中間周波増幅管遮蔽格子塞流線輪 第二局部發振管同調蓄電器 a 第二局部發振管同調線輪 欠 番 b 第二局部發振管同調蓄電器 第二局部發振管格子蓄電器 c 欠 番 第二局部發振管格子抵抗器 50kΩ (D-05型) d 第二局部發振管格子蓄電器 音色調整器 e 第二局部發振管格子抵抗器 第二局部發振管 UZ-6C6  音色調整器 第二局部發振管陽極直列抵抗器 3kΩ (D-05型)  第二局部發振管 第二局部發振管陽極分圧抵抗器 甲 50kΩ (D-05型) 第二局部發振管陽極直列抵抗器  乙 第二局部發振管陽極圧抵抗器 500kΩ (D-05型)  第二局部發振管陽極分圧抵抗器 甲 電信電話轉換器 乙  第二局部發振管陽極圧抵抗器 0.001μF 第二低周波増幅管格子結合蓄電器  電信電話轉換器 第二低周波増幅管格子抵抗器 100kΩ (D-05型)  第二低周波増幅管格子結合蓄電器 第二低周波増幅管 UZ-6C6  第二低周波増幅管格子抵抗器1kΩ (D-05型) 第二低周波増幅管陰極直列抵抗器  第二低周波増幅管 欠 番  第二低周波増幅管陰極直列抵抗器 第二低周波増幅管遮蔽格子分圧抵抗器 100kΩ (D-05型)  欠 番 第二低周波増幅管遮蔽格子側路蓄電器 0.01μF  第二低周波増幅管遮蔽格子分圧抵抗器 0.001μF 第二低周波増幅管陽極直列抵抗器 3kΩ (D-05型)  第二低周波増幅管遮蔽格子側路蓄電器 0.01μF 第二低周波増幅管陽極側路蓄電器 1μF 第二低周波増幅管陽極直列抵抗器  500kΩ (D-05型) 第二局部發振管陽極側路蓄電器 0.01μF  第二低周波増幅管陽極側路蓄電器21 0.00025μF 低周波出力變成器  第二局部發振管陽極側路蓄電器 0.01μF 低周波出力變成器並列蓄電器 0.01μF X2  低周波出力變成器 Ut-6B7 受話器ジヤツク 500kΩ (D-05型)  低周波出力變成器並列蓄電器 第二局部發振管結合蓄電器  受話器ジヤツク 0.00025μF 電源開閉器 500kΩ (D-05型)  第二局部發振管結合蓄電器 受信機接栓受 3kΩ (D-05型)  電源開閉器 電圧測定口 1kΩ (D-05型)  受信機接栓受 空中線抵抗器 500kΩ (D-05型) 0.01μF 甲  電圧測定口 空中線結合蓄電器 100kΩ (D-05型) 空中線結合蓄電器 乙  空中線抵抗器 100kΩX2(D-05型)  空中線結合蓄電器 甲 1μF  空中線結合蓄電器 乙 3kΩ (D-05型) 100kΩ (D-05型) 500kΩ (D-05型) 500kΩ (D-05型) 0.01μF 30kΩ (D-2型) 50kΩ (D-2型) 10kΩ K L M is the only one I’ve personally seen, apart from Takashi Doi’s example in the Yokohama Museum. So if you see, or even hear of, a Chi that someone wants to dispose of, snap it up! Supplementary information Unlike the Chi Mark 1 radio set/ receiver, the Chi Mark 1 receiver does not have a control that changes the amplification level of the LF stage. For telephone (A3) reception with this receiver, the manual (RF/IF) gain adjustment should set the receiver operation to maximum gain so that the AGC will operate correctly. However, setting the RF/IF gain adjuster to maximum gain is difficult, as this produces excessive sound output. In H I J K 番號 名 稱 電源開閉器諸 元 1μF  低圧側高周波側路蓄電器 甲 電池接栓受 1μF  電源開閉器 低圧側高周波塞流線輪 甲 0.1mH  低圧側高周波側路蓄電器 甲 0.1mH 低圧側高周波塞流線輪 乙 低圧側高周波側路蓄電器  乙 低圧側高周波塞流線輪 甲 0.01μF 低圧側高周波側路蓄電器  丙 低圧側高周波塞流線輪 乙 0.01μF  低圧側高周波側路蓄電器 乙 直流變圧器 高圧側側路蓄電器 甲  低圧側高周波側路蓄電器 丙 0.01μF 50kΩ (D-05型) 高圧側側路蓄電器 乙  直流變圧器 0.01μF  高圧側側路蓄電器 甲 高圧ヒユーズ 100mA UZ-6C6  高圧側側路蓄電器 乙 高圧側高周波塞流線輪 甲 6mH 3kΩ (D-05型) 乙  高圧ヒユーズ 高圧側高周波塞流線輪 6mH 50kΩ (D-05型)  高圧側低周波側路蓄電器 甲 高圧側高周波塞流線輪 甲 1μF 500kΩ (D-05型)  高圧側高周波塞流線輪 乙 高圧側低周波塞流線輪 3.5H 高圧側低周波側路蓄電器 甲  高圧側低周波側路蓄電器 乙 10μF 0.001μF  高圧側低周波塞流線輪 高圧側低周波塞流線輪 3.5H 100kΩ (D-05型)  高圧側低周波側路蓄電器 丙 高圧側低周波側路蓄電器 乙 10μF UZ-6C6  高圧側低周波塞流線輪 受信機接栓受 1kΩ (D-05型)  高圧側低周波側路蓄電器 丙  受信機接栓受 100kΩ 番 (D-05型)  欠 0.01μF  交流電源接栓受 3kΩ (D-05型)  欠 番  電源開閉器 1μF  交流電源接栓受 1A  交流電源側ヒユーズ 0.01μF  電源開閉器  欠 番  交流電源側ヒユーズ  電圧轉換器 21 乙 5V 2A 6.3V 3A 0.01μF X2  欠 番 80-200V 240V  電源變圧器 X2 60mA  電圧轉換器 乙 150V  電圧計  電源變圧器  電圧計倍率器  電圧計 KX-80  整流管 100mA  整流管直流側ヒユーズ  電圧計倍率器  整流管  欠 番 500kΩ (D-05型) 甲  整流管直流側ヒユーズ 30H  高壓電源平滑線輪 番 30H  高壓電源平滑線輪 乙  欠  高壓電源平滑蓄電器 甲  高壓電源平滑線輪 甲 1μF  高壓電源平滑蓄電器 乙  高壓電源平滑線輪 乙 10μF  高壓電源平滑蓄電器 丙  高壓電源平滑蓄電器 甲 10μF 高壓電源平滑蓄電器 乙  30kΩX2 (D-2型)  整流管直流側並列抵抗器  高壓電源平滑蓄電器 丙  受信機接栓受  整流管直流側並列抵抗器  受信機接栓受 印ハ予備品又ハ材料ヲ有スルモノヲ示ス 諸 元                   practice, a workable RF/IF gain setting does not allow the AGC function to be fully utilised. For this reason, compared to Chi Mark 1 Radio Set/Receiver, this receiver does not give optimum performance when listening to A3 signals. Thanks go to: • Takashi Doi, founder of the Yokohama WWII Japanese Military Radio Museum (see their website – www. yokohamaradiomuseum.com). • Ray Gillett of the Historical Radio Society of Australia (HRSA) for the loan of this very rare radio. • Brian Goldsmith of the HRSA. • You can find more details on the Chi receiver (in Japanese) at: http:// SC minouta17.web.fc2.com/ 印ハ予備品又ハ材料ヲ有スルモノヲ示ス O N L M P N O Radio TV & Hobbies The Complete Collection on USB Every issue from April 1939 to March 1965 If you're into anything vintage it doesn't get any better than this scanned collection of every single issue of Radio & Hobbies, and Radio TV & Hobbies magazines before they became Electronics Australia. It provides an extraordinary insight into the innovations in radio and electronics from the start of WW2 to the early transistor era! PDF Download $50 SC2950: siliconchip.com.au/Shop/3/2950 USB + Download $70 SC6142: siliconchip.com.au/Shop/3/6142 Postage is $10 within Australia for the USB. See our website for overseas & express post rates. siliconchip.com.au Australia's electronics magazine October 2023  105 9 0 1μF 0.1mH 0.1mH 0.01μF 0.01μF 0.01μF 0.01μF 100mA 6mH 6mH 1μF 3.5H 10μF 3.5H 10μF 1 1A 80-200V 5V 2A 6.3V 240V X2 60 150V 2 KX-80 100mA 30H 30H 1μF 10μF 10μF 30kΩX2 (D-2型 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Causes of mains switch arcing I have a small coffee grinder. When I switched it off recently, the switch sparked massively, and the house circuit breaker tripped. This has never happened before or since and there is nothing wrong with the coffee grinder. It still works perfectly without any more sparks. I checked the wiring and all the wires were well separated and away from the plastic body of the device. Also, there was no sign of sparking inside the body or around the motor. Is it possible that at the instant I switched off the machine, the back EMF was exactly 180° out of phase with the mains and caused a short? The switch didn’t smell burnt after the event and still works perfectly, although the spark was very big. It doesn’t spark at all normally as the motor is relatively small. Also, the motor doesn’t smell burnt. Even if the switch had coffee dust in it (which it didn’t), why did the circuit breaker blow? (C. R., Tuebingen, Germany). ● We can’t see how the back-EMF can be so significant that it can cause what you describe. We think it is more likely that there is an intermittent 106 Silicon Chip motor fault causing a short circuit to the Earthed frame. However, readers might have a better idea, in which case we ask them to please email a suggestion. In-circuit capacitor testing with ESR Meter I am very interested in the Arduino-­ based LC/ESR Meter design (August 2023; siliconchip.au/Article/15901). I have one question, though: can it perform in-circuit testing of electros? (G. D., Burleigh, New Zealand) ● The designer, Steve Matthysen, responds: generally, the ESR function can measure in-circuit ESR values (for de-energised circuits!) and should provide near-accurate readings. It comes down to applying the theory that capacitors block direct currents whilst presenting a low impedance to alternating currents. The ESR test current is very low and should not generate any inductance-­ related effects. However, if the returned ESR result is low, that does not necessarily mean the capacitor is good. Any source of a very low DC resistance across a bad capacitor will also result in a misleading low ESR value. Hence, one should still confirm that the expected low ESR result is not due to a faulty component connected to or across the capacitor that may have developed a short or near short circuit (a resistor, diode, transistor, the capacitor itself having developed an internal short etc). When testing electrolytics in-­circuit, one should measure the DC resistance across the capacitor, followed by an ESR reading. If the DC resistance is relatively high in conjunction with a low ESR reading, one may rule out a problem with the capacitor’s effective series resistance. However, if the DC resistance is low (less than the expected ESR value), the ESR test must be done with the capacitor isolated from the rest of the circuit. As a reminder, to prevent possible Australia's electronics magazine damage to the tester, always make sure the circuit under test is not powered up, and the capacitor to be tested has no residual charge across it. VGA PicoMite assembly instructions I want to build the VGA Pico­Mite from your SC6417 kit (July 2022 issue; siliconchip.au/Article/15382). I am an electronics newbie. Does the kit come with assembly instructions? (V. T., via email) ● We have comprehensive assembly instructions in our July 2022 issue to suit beginners or experienced constructors. However, if you don’t have a copy of that magazine, Geoff Graham also has instructions on building his designs on his website. You can find his instructions for assembling the VGA PicoMite at https://geoffg.net/picomitevga.html (scroll down to the bottom; there is a “Construction Pack” download listed under “Other Downloads”). How were vibrators tested and calibrated? Dr Hugo Holden’s recent articles on vibrators were interesting (June-­ August 2023 issues; siliconchip.au/ Series/400). When he described testing its performance with an oscilloscope, it made me wonder: how were vibrators tested and calibrated back when they were new? Most people would not have had oscilloscopes. I came across a document from RCA-Victor Co that showed one way of testing vibrators with a battery, transformer and several analog meters. (R. H., Ferntree Gully, Vic) ● Dr Hugo Holden responds: there were once test rigs for checking and setting up vibrators. Of course, none were as good as using a scope. But many radio repair shops, in the early days at least, did not have one as they were an expensive luxury, so other simple test methods were deployed. It was not dissimilar to the early test siliconchip.com.au setups for things in automotive electronics in various repair workshops, such as early dynamo voltage regulators (as another example), which used coils, moving armatures and contacts and relied on principles of electromagnetism. Most of it was pretty clever, including temperature properties of return springs on the armatures that compensated for the tempco of copper wire. Tricky metallurgy was also king, both with the springs and the B-H curves of the particular iron cores. The engineers knew exactly what they were doing and did it all from a thorough understanding of the basic electrical sciences and using slide rules. They had to study the molecular theory of magnetism, Ampere’s theory of magnetism, Gauss’ law, Faraday’s laws, spring metallurgy etc. I never underestimate the genius and creativity of vintage electromagnetic creations. But these are not the sort of things you can run in a SPICE simulator these days. As the years went by, it became evident to people who figured out how these vintage electromechanical devices like vibrators worked that calibrating and checking them was better done with the aid of the ‘scope than any other method. In modern times, many of the electromagnetic principles of these archaic devices have fallen into obscurity and are not taught in modern tech schools. Most designers of common apparatus, even audio amplifiers, avoid transformers now like the plague. Yet before the semiconductor age, copper coils, iron laminations and electromagnetism ruled the roost. Programming dsPICs out of circuit Do you have any tips on programming the dsPIC33FJ128GP802 and dsPIC33EP512MC502 ICs used in the Spectral Sound MIDI Synthesiser project from June 2022 (siliconchip. au/Article/15338)? I received the programmed ICs from you in the kit I purchased, but I wanted to update them to the latest firmware. I was able to successfully program the PIC18LF25K50 IC with the clone PICkit 3 programmer I have. However, when trying to program the dsPIC33xx chips, I receive a “Target Device ID (0x0) is an Invalid Device ID” message. siliconchip.com.au The chips are connected to the programmer on their own and not using ICSP. Option “Power target circuit from PICkit3” is ticked. I’ve tried the following with no luck: • Two different PICkit 3 clones. • Programming on Windows and Mac. • Adjusting the “Voltage Level” between 3.0V and 3.5V in MPLAB IPE. • Using the standalone Pickit 3 programmer v3.10. (D. P., Rush, Ireland) ● It sounds like the problem is in the connections to the chip and not your software or programmer. The dsPIC chips require a bit more complex programming rig than the PIC18 due to their internal core regulator that won’t operate correctly without an external capacitor. That capacitor must also have specific properties (minimum capacitance of 10μF, maximum ESR of 1W). Note that we just published a PIC Programming Adaptor that could be used for these chips (September 2023; siliconchip.au/Article/15943). As these chips usually need several bypass capacitors to operate, they are best programmed on a board with a socket, those capacitors and a header for the PICkit. The connections we use are: VDD: pin 13 & pin 28 GND: pin 8, pin 19 & pin 27 MCLR: pin 1 PGD: pin 4 PGC: pin 5 VCAP: 10μF+ tantalum or ceramic capacitor (ideally more like 47μF) between pins 19 & 20 It’s also a good idea to have smaller bypass capacitors (eg, 100nF) between pins 8 & 13 and (less importantly) pins 27 & 28. That Programming Adaptor we published recently provides all these connections and capacitors, along with a ZIF socket for the chip to be programmed and a header for the PICkit. Micromite Plus SD card problem I am building the slot machine from the May 2022 issue (siliconchip.au/ Article/15310). However, no matter what I try, any attempt to list the files on the SD card (using the FILES command) results in “Error : SD card not found”. Australia's electronics magazine I checked that the microcontroller pin 22 changes state depending on whether or not an SD card is installed. Pin 21 changed state depending on whether or not an SD card is installed during one test session but not on another. I tried two SD cards and have tried reformatting with different formatting programs. The SD cards I am using are 32GB formatted FAT32 Verbatim Premium V10. (R. M., Higgins, ACT) ● There are really only four things that can go wrong: 1. The soldering on the SD card socket or microcontroller. 2. The configuration of the Micromite. 3. Problems with the SD card itself. 4. Interference from the display or another SD card. For #1, check pins 2-7 of the socket and pins 4, 5, 21 and 47 of IC1 carefully to ensure they are soldered to the board and there are no bridges between them. The fact that the pin 21 state changes inconsistently suggests a bad solder joint. For #2, check that the OPTION SDCARD 21, 22 command has been executed correctly (you can use OPTION LIST to verify that). #3 is more or less ruled out by your trying multiple cards, but you should try different types to be sure. For #4, note that you can’t have SD cards in both sockets at once if you’ve soldered CON7 to connect the holder on the screen. A solder bridge on that header could also cause problems. While it’s unlikely to be a problem, the touchscreen shares the SPI bus with the SD card holder, so you could try unplugging that to check that it isn’t interfering. Using PIC USB pins as digital I/Os I have a question regarding the PIC16F1455 8-bit microcontroller you have used in some of your projects. I wish to use the RA0 and RA1 pins as normal inputs, so I need to turn off the USB module. To save me from reading through all the USB module registers, can you tell me which ones must be changed to disable USB? (L. K., Ashby, NSW) ● As with most similar chips, the internal USB module is disabled by default. The data sheet notes that the USB module should only be enabled October 2023  107 once the clocks have been appropriately set. Therefore, you don’t need to do anything special to use the USB pins as I/O pins. If you want to make sure, you can clear the USBEN and SUSPND bits of the UCON register, but we don’t think that is necessary. Increasing CD Spot Welder voltage Regarding the Capacitor Discharge Welder project from March & April 2022 (siliconchip.au/Series/379), the 39mF cap that is the primary example capacitor in the energy module is given as Mouser reference B41231A5399M002. That refers to a three-pin part. It should be B41231A5399M000, the equivalent two-pin part that will fit your PCB. I double-checked this by looking at the data sheet. I started building my own CD Welder about a year before you published your version. My version was going to run a smaller total capacitance (660mF) at a higher voltage (30V). That would have given a faster and cooler weld but at a higher risk of blowing up the Mosfets. I was also going to charge my capacitors at 50Hz from a switched bridge (part IXYS VHFD37-08IO1), with the SCR gates just held at a static threshold target voltage. The SCRs in the bridge would have been totally on or totally off, so it should have been efficient from a thermal viewpoint. Maybe that would have worked, or maybe it also would have blown up! Now that I’ve finally gotten back to this, I’ve decided that there are enough improvements in your triggering approach that I’ve abandoned my own PCBs and bought boards from the Silicon Chip Online Shop. I would still like to use my collection of 22mF 35V capacitors. It’s hard to get a good handle on the peak discharge current because some of it will be held back by inductance rather than pure resistance. Could the voltage be tweaked a little higher sufficient to use a 660mF total bank, or is the design already pushing up against the operational current limits of the Mosfets? Were there any prototypes that did blow up? (M. J., St Lucia, Qld) ● The designer, Phil Prosser, responds: I am surprised that a wrong part number made it into the article. Sorry about that. Unfortunately, the distributor’s website has the wrong image for that part (it shows a twopin capacitor, not a three-pin type), which misled us. The inductance in the system is minimised to keep back-EMF under control. Resistance is the primary thing that limits current, although it is true that there will always be some inductance. The recommended cable design has the two conductors held parallel like figure-8 cable. Even with this, when you make a weld, you can feel the inductive constriction make the cables jump! The specified Mosfets have a voltage rating of 40V, so 35V would be OK, but you’ll want to make sure your circuit can’t exceed that. The charge circuit can tweaked to limit at 30V or 35V by increasing the value of the 27kW resistor slightly until full clockwise rotation of VR1 stops charging the capacitor bank just below 35V (you could test with a couple of 50V caps until you’ve verified that). There is a spreadsheet on which I did a lot of analysis for current ratings that you can download (siliconchip. GPS-Synchronised Analog Clock with long battery life ➡ Convert an ordinary wall clock into a highlyaccurate time keeping device (within seconds). ➡ Nearly eight years of battery life with a pair of C cells! ➡ Automatically adjusts for daylight saving time. ➡ Track time with a VK2828U7G5LF GPS or D1 Mini WiFi module (select one as an option with the kit; D1 Mini requires programming). ➡ Learn how to build it from the article in the September 2022 issue of Silicon Chip (siliconchip. au/Article/15466). Check out the article in the November 2022 issue for how to use the D1 Mini WiFi module with the Driver (siliconchip.au/Article/15550). Complete kit available from $55 + postage (batteries & clock not included) siliconchip.com.au/Shop/20/6472 – Catalog SC6472 108 Silicon Chip Australia's electronics magazine siliconchip.com.au au/Shop/6/6306). You should be able to use that to check the limits at 35V. I expect that if you have 22mF caps and don’t short the busbars, it will be OK, but it will be marginal if you drop a spanner across the busbars. At 25V, the Mosfets can actually handle the busbars being shorted at the box on paper (although I never actually tested that, as I am not bonkers). I tried killing the thing and had a couple of spare modules, but I failed to destroy the Mosfets. I ran tests smashing a single module into silly loads at ridiculous rates of fire. The Mosfets stay stone cold as they are either off or very hard on with the drivers we used. You are unlikely to actually need to use this at 35V and 660mF. That is 400J, more than you should need, and it will likely blow holes in metal strips. So you will probably have that voltage turned down almost all of the time anyway. The design allows you to stack as many modules as you want, within reason. So, if I were you, I would build it and see how you go. I expect the spreadsheet will say you are fine with even a modest cable length. Treat those busbars with the respect they demand. Remember that the cables are part of the system design. 1m cables will dominate your current limiting. Another CD Spot Welder query I have a question regarding the Capacitor Discharge Spot Welder project. I regularly repack Milwaukee and Makita 18V packs with new original cells. Until now, I have had to replace the original nickel-plated 0.150.20mm copper strapping with pure nickel or nickel-plated steel strapping. Would your capacitor discharge welder, with the maximum ESM storage designed, be capable of spot welding the original style copper strapping? Using copper strapping will ensure the packs return to their original load performance. (R. E., Dover Gardens, SA) ● Phil Prosser responds: that is not something I have tried. Copper has a high thermal conductivity and capacity, so I can see it being a challenge. If you have a sample of the copper straps, please send it to the Silicon Chip PO box, and I can see whether I can achieve decent welds with my prototype. Multiple Arduino libraries being detected Can you help with this error I get when uploading the Arduino_UVI_ meter_sketch.ino sketch for the May 2023 article on the UVM-30A Ultraviolet Light Sensor? The error message says (in part): Arduino_UVI_meter_sketch:35:13: error: no matching function for call to ‘LiquidCrystal_I2C::begin()’ Multiple libraries were found for “LiquidCrystal_I2C.h” Used: C:\documents\Arduino\ libraries\LiquidCrystal_I2C Not used: C:\documents\Arduino\ libraries\LiquidCrystal Not used: C:\documents\Arduino\ libraries\LiquidCrystal_I2C-master Not used: C:\documents\Arduino\ libraries\Newliquidcrystal_1.3.5 I am not well-versed in Arduino. Can you advise me on how to get this program working? (J. H., Nathan, Qld) ● It looks like you have four different LiquidCrystal_I2C libraries installed. Unfortunately, there are a few variants around, and we have used different ones for other projects. We suspect that the Arduino IDE is Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed siliconchip.com.au Australia's electronics magazine October 2023  109 automatically choosing the wrong one. This is a bit of a known problem with Arduino. The one you want for this project is called “LiquidCrystal_I2C-master”, but it seems to be using the one called “LiquidCrystal_I2C” instead. We suggest temporarily moving the “LiquidCrystal_I2C” library to another location (to hide it), then restarting the Arduino IDE (to let it see the library change). After that, try recompiling the sketch. If that doesn’t work, try installing the version of the library that you can download from: https://github.com/fdebrabander/ Arduino-LiquidCrystal-I2C-library Jim used that library for his Wideband Digital RF Power Meter, and it matches the code in the Arduino_UVI_ meter_sketch.ino sketch. Currawong valve amp mystery solved I recently purchased the last available Altronics kit of the Currawong Stereo Valve Amplifier in Australia (November 2014 to January 2015; siliconchip.au/Series/277)! It was a good kit, very well thought out and nicely designed. Very easy to build. I have a problem that I am struggling to find an answer to. The voltage across the 330W resistors continuously climbs. It starts at the correct voltage, 22V. Over time, it increases to over 60V! This causes the resistors to overheat as they are dissipating around 12W each. It also eventually causes the slow-blow 1A fuse to blow. I’ve triple-checked everywhere and can’t find any misplaced components or silly mistakes. The amplifier works well apart from that; it sounds really good and functions as it should. Any help you can offer would be greatly appreciated! (L. C., Welshpool, WA) ● The four 330W 5W resistors are the cathode resistors for the four 6L6/ KT66 valves in the push-pull output stage. They help to obtain the correct DC bias conditions for those output valves, in combination with the 1MW grid resistors to ground. As the current through each valve increases, so does the voltage across the 330W resistor, making the effective grid bias negative and eventually stabilising at a reasonable quiescent current. Obviously, that stabilisation is not happening. Check if the pin 5 grid voltages for the 6L6/KT66s are drifting upwards over time. You can check that at the left-hand ends of the 10kW resistors between the 12AX7s and 6L6s, but be careful not to slip and short anything out! The short metal links next to LK4 and LK5 are at ground potential, so they can be used for the other probe connection. If those voltages are drifting up, try reducing the values of the 1MW resistors between the 12AX7s and 6L6/ KT66s to, say, 470kW. You can test that initially by clipping or soldering a second 1MW resistor across those resistors. If that works, you should also change the nearby 220nF capacitors to 470nF to avoid affecting the frequency response, but verify that it fixes the drift first. Accurate 6-digit GPS Clock module replacement I built the Dead-Accurate 6-Digit GPS-Locked Clock from May & June 2009 (siliconchip.au/Series/37), but the GPS module failed and I need to replace it. I purchased a V.KEL VK2828U7G5LF module from your Online Shop. The baud rate for the old GPS module was 4800 but this V.KEL module defaults to 9600. What steps do I need to take to make this work on my old clock? The V.KEL module does not work when connected where the old one was. (N. S., Nambucca Heads, NSW.) ● You can reprogram the VK2828U7G5LF to operate at 4800 baud, although the process is a bit involved. First, you need a serial adaptor, such as a USB/serial converter, to connect it to a computer (at the default 9600 baud rate). Then you need a terminal program that can send binary data entered as hexadecimal numbers. The VK2828 data sheet (siliconchip.au/link/ablx) shows the hexadecimal data you need to send to set it to 4800 baud on page 14. The u-blox u-center software they show in the data sheet might be able to do it but we are not sure. This web page lists several programs that you could use: siliconchip.au/link/ablw That page says you can use the following Windows programs to send the data: RealTerm, Termite or comDebug. 110 Silicon Chip Australia's electronics magazine If the bias voltage is not increasing, the only other fix we can think of is to increase the values of those 330W 5W resistors (eg, you could try 470W). The higher the value of those resistors, the more negative the grid bias becomes and, at some point, the current should stabilise at a reasonable value. You would have to monitor the dissipation closely; the higher values would tend to increase dissipation. Still, hopefully, that would be more than offset by the reduced current due to reduced bias. The correspondent got back to us shortly after we sent this answer, stating: “You wouldn’t believe it; I forgot to install those little links you were referring to. It is working 100% now.” Those links connect the 1MW grid bias resistors to ground, so that would explain the bias drift! BF194 transistors are still available I am trying to restore a vintage BWD 539A oscilloscope to operating condition. My fault finding, so far, has located three open-circuit BF194 transistors. I have sent a few emails to local (New Zealand) suppliers, but none can supply these or even close equivalents. Please advise me on what commonly available transistors I can replace these with. At the moment, all the faulty transistors are in the ‘Y’ (vertical) timebase amplifier. (P. W., Pukekohe, NZ) ● Wiltronics in Alfredton, Victoria is currently selling BF194s for 35¢ each. See www.wiltronics.com.au/ product/4985 There might be equivalent replacements, but if you’re fixing vintage gear, we think it’s better to stick with the original parts when it’s reasonable to do so. Multi-Spark CDI unit not sparking Are there any notes on the High Energy Multi-Spark CDI project from 2014 (siliconchip.au/Series/279)? I have not found any. I ask because I have not managed to get mine working. The 300V DC supply is OK, but IC3 refuses to oscillate. I have found one error in the layout drawing: D7 is upside down. The continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales Lazer Security KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au V I S I T T H E T R O N I X L A B S par ts clearance store for real savings on parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com PCB PRODUCTION MAGAZINE GIVEAWAY PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au Readers in Ryde, NSW; Kirwans Bridge, Vic; & Caloundra Qld have collections of Silicon Chip magazine they want to give away. If you’re interested, please email us at silicon<at>siliconchip.com.au For Quality That Counts... After 38 Years, I am looking to move and semi-retire. Lazer Security needs a young and dedicated person to evolve and grow. We are currently based in Wolli Creek, NSW and we sell new components, unused (recycled) components and kits with an emphasis on LED lighting. If you are interested in purchasing the business from me, please contact tony<at>phoslighting.net SILICON CHIP ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have been sold. See photos (recently updated): siliconchip.au/link/abl3 Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine October 2023  111 circuit diagram has it drawn correctly (anode to pin 2 of IC3). I initially suspected I had a faulty L6571 (IC3). I have since replaced it with a new one, but it made no difference. (A. C., Kelso, NSW) ● Notes & Errata can be viewed from siliconchip.au/Articles/Errata – in this case, there are no relevant entries. Diode D7 is orientated correctly in the circuit diagram; it is just that the 180kW resistor and series-­connected diode are transposed. The circuit operation is the same. So long as IC3 has at least 10.5V as a supply, it should operate. Otherwise, check the component placement, soldering and for any shorts between adjacent connections. Also verify that your replacement L6751 is the A version, not the B version. We supply the A version in our parts set as that is what the design requires. This is a popular project with hundreds built and few complaints, so we don’t think it has any major flaws. You Advertising Index Altronics.................................57-60 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes..........................OBC icom Australia............................. 10 Jaycar.............................. IFC, 9, 11, .........................26-27, 43, 86-87, 97 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 likely have either a dud component or a placement/soldering problem. Pressure sensor for Ignition System I am considering buying the parts you have available for the Programmable Ignition System for Cars (MarchMay 2007; siliconchip.au/Series/56) on your website. I am having trouble finding the part number for the PCB-mounted pressure sensor and where I could purchase it. Do you know of anywhere there still might be a complete kit available? (P. H., Blackburn, Vic) ● All kits for that project have been discontinued. The Sensym pressure sensor is unavailable, so we recommend using a MAP (Manifold Absolute Pressure) sensor instead, available from a salvage yard/wrecker. Use a 1bar sensor for naturally aspirated engines or a 2bar sensor for boosted engines. The article shows how to use a MAP sensor. Although the kits have been discontinued, the major parts like the PCBs and programmed microcontroller are available from the Silicon Chip shop (siliconchip.au/Shop/?article=2233). You should be able to obtain the rest from electronic component retailers. Car radio antenna amplifier wanted Did Electronics Australia ever publish an antenna amplifier for AM reception in car radios etc? I can’t seem to find any! I still have a stack of EA magazines dating back to the mid-1960s. I loved EA back in the day. I first saw EA in the library when I attended technical school in the 1960s. I was so fascinated by the articles that I began Mouser Electronics....................... 4 SC GPS Analog Clock............... 108 SC Radio TV & Hobbies............ 105 Silicon Chip PDFs on USB....... 109 Silicon Chip Shop.................88-89 Silicon Chip Subscriptions........ 71 The Loudspeaker Kit.com............ 6 Tronixlabs.................................. 111 Wagner Electronics..................... 93 112 Silicon Chip Errata & Sale Date for the Next Issue Microchip Technology.................. 7 to make some of the projects. I was lucky that Mum got me a Scope soldering iron and a multimeter for my 13th birthday (a long time ago). I eventually left school and gained an apprenticeship as a radio and TV technician the year Man walked on the moon. Unfortunately, with the later demise of the TV repair industry, I had to switch trades. It’s sad that we lost all of the commercial manufacturing of electronics, TVs, radios etc. I did work at Flexdrive near Melbourne for a while; they made electronic speedos, trip computers and integrated electronics for the automotive industry (all Australian designed and built). They are gone too. I remember an article in EA about Fairchild semiconductor manufacturing in Australia; they’re also gone! Believe it or not, Dyne is still making transformers in Melbourne. I remember Leo Simpson’s articles and built many projects that interested me. (T. R., via email) ● EA published several antenna amplifiers for AM radio. The following was taken from the index: siliconchip. au/Static/EA%20Projects • 2/AE/48 Low Cost Booster for AM Reception (antenna) (August 1994) • 2/AE/49 The ‘Miracle’ AM Antenna (November 1996) We have also published the following projects: • Simple Car Antenna Amplifier (December 1988 issue; siliconchip.au/ Article/7574) • Passive Loop Antenna For AM Radios (June 1989 issue; siliconchip. au/Article/7458) • AM Loop Antenna & Amplifier (October 2007 issue; siliconchip.au/ Article/2398) • AM Broadcast Band Portable Loop Antenna (January 2009 issue; siliconchip.au/Article/1280) SC Arduino LC/ESR Meter, August 2023: there are two errors in the wiring diagram, Fig.3. (1) The wires from A0, A2 & A3 on the shield should go to A1, A2 & A3 on the Arduino, respectively, not A0, A1 & A2. (2) The connections to switch S1 for the 10kΩ resistor and grey wire that goes to the GND terminal on the Arduino should be swapped. The leftmost and rightmost connections for S1a in Fig.2 should also be swapped. CD Spot Welder, March & April 2022: in Table 1 on page 28, the second entry for the 39mF capacitors has the wrong part number/ link to Mouser. It should be https://au.mouser.com/ProductDetail/871B41231A5399M000 (not -002). Next Issue: the November 2023 issue is due on sale in newsagents by Thursday, October 26th. Expect postal delivery of subscription copies in Australia between October 25th and November 13th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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